Basically this

Ive seen clothes bleed like twice, once was a set of dark sheets I washed for the first time, which bled a shitload, and the other was a cheap promotional shirt I bleached which turned the water black.

I don’t separate colours, only new clothes I put in with towels, sheets or clothes that I wouldn’t care if colour bled.

I never wash with hot water, only warm or cold. Low heat dry and cold water washing is really the best effort-for-performance to get your clothes to last, you can hang dry some of them but I personally can’t be arsed.

I keep and wash my whites separate in hot or warm water. Everything else goes together in cold water. Wool stuff gets air dried, while the rest gets the dryer.

Add a cup of white vinegar to the wash with the clothes if anything is extra smelly, during the wash cycle/beginning.

Easy. I only have black clothes. If there’s bleeding, I can’t see it.

I have hot wash for towels and bed stuff. Cold for literally everything else. I’ve never had anything bleed, even new stuff.

Generally, after two or three washes, you don’t need to separate any more. You really only get bleeding with new fabrics, and even then only with cheap fabrics. As an example, if you order Amazon’s cheapest towels, not only wash them separately, wash them before you use them unless you want the color on you. But even those eventually stop bleeding.

If you’re going to sort, the way I was taught is to separate colors from whites, with blacks being a separate load as well. The idea is that the bleed from any of the colors isn’t going to be enough to matter since there’s already dye present, which means there’s less ability to take on new dye. That can fail, and you end up with the color of things changed. So you still always test any new fabrics before throwing them in with other colors. But, generally speaking, if you don’t have the time, don’t have enough of that color to make a load, or just don’t care about color change, the risk of any color change being huge is low nowadays.

The only reason to do blacks on their own is that it mutes other colors when it bleeds.

If you’re really paranoid about it, either do each color on their own, or make batches where the colors bleeding wont be as significant. Like, blues and greens, or greens and yellows. Any bleed that does happen like that won’t be as noticeable, if it is at all.

But I never saw in all my years washing other people’s clothes anyone that had enough of every color to make multiple loads without waiting way too long between washings. Maybe in a really big family you’d pile up enough mixed colors in a week or two to make full loads of multiple single colors, or even two colors.

You’re also usually okay washing bed sheets and clothes together, though you can pull out stuff with zippers and metal buttons if you take want to maximize life spans of the rest. Being real though, making a load of those together is just going to shift which items get the teeny, tiny extra bit of wear from the fasteners. It might be worth it with heavy denim, but I wouldn’t and don’t bother personally.

Now, as far as types of fabric, you run into some issues. Good wool might need its own special care, but you’d want to refer to the label to determine that. Silk is hand wash only unless you like ruining silk. Cotton, linen, polyester, rayon, and nylon can all be washed with any other fabrics, no issues. At worst, you might run into a little extra pilling with the natural fabrics being washed together, but I’ve sever seen it actually happen more than what the fabrics do on their own just from being washed.

You specified merino wool. Afaik, you should machine wash as the default. But wash in cold only, and go with the bare minimum of detergent. Make sure you pull it out as soon as possible to reduce wrinkling, and hang to dry. Yeah, in theory your can machine dry merino, but if you’re asking this at all, you want to maximize the life and appearance of your clothes, so hang to dry.

Hand washing works as well as you’re willing to put in the work on, but wool tends to hold on to oils and sweat residue more than most fabrics, so you have to really work at it compared to something like cotton that gives up oils as easily as any natural fabric will.

If you’re having a problem with lint on your laundry, do your towels and other terry fabrics on their own. Most of the time, that’s where excessive lint is coming from. But if you aren’t having that issue, don’t worry about it.

A lot of separating of types of fabric goods, like sheets from clothes, isn’t about what they’ll do to each other or needing different types of care, it’s about convenience. Folding and storing sheets all at once is easier than dealing with a mixed load, as an example. You do benefit in being able to run things like towels hotter than you’d want with most clothing, but it’s a marginal benefit imo.

My laundry isn’t sorted much at all unless I get new stuff. Towels and washcloths and the like stay in their own loads. Clothes together, with only a few extra heavy fabrics on their own (like my canvas outdoors stuff and gis). Bed linens tend to be a load of their own since there’s two beds worth of those at a time, there’s just not room for more. But, when that’s not the case, I tend to throw them in with towels.

And, as always, check your labels. While it isn’t a guarantee, the recommended care on them really is the best pick. You’ll run into some chinese fabrics where it’s just generic instructions, but those tend to default to the least wear options anyway, so it won’t hurt anything, it just isn’t ideal. The companies using outsourced labor still specify the label contents, so it’s only when it isn’t a brand at all that you see the generic labels.

I also tend to recommend that you avoid fabric softener. They really don’t do anything useful, they cost extra, and a lot of people are sensitive to them and don’t realize it. If you’re getting itchy a lot, and you’re using them, try a few weeks without. Same with rashes where the fabric is extra close to skin.

You’re overthinking it.

Modern fabric dyes are a lot better than 40 years ago. Like, don’t wash something dark the first time with a bunch of white stuff, but after the first wash or two it definitely doesn’t matter

We do: my wife’s stuff and our t-shirts with pictures for delicates wash and literally everything else goes in on a standard wash cycle.

Red, orange, yellow, green, brown in one pile. Blue, grey, black in a second pile. White stuff in a third.

I don’t

I don’t think I do it correctly tbh, but since I have to drive to the laundromat to do my laundry, and pay out the ass for it ($12 per fucking load!!), all I want is to get in and out of there as fast as humanly possible. So I have two piles, one for all my clothes regardless of color or material, and the other for sheets and towels, regardless of color. I haven’t noticed any colors bleeding or extra degradation, and my clothes generally look pretty undamaged and crisp. I also typically use the hottest cycle for everything, which again, probably isn’t great, but it seems to work for me.

Bleach pile, no-bleach pile, performance outdoor pile (wool, polypro, nylon/down, whatever)

E: oh, and extra-bleach pile: kitchen towels, dog towels

I don’t.

And haven’t for 30+ years. I also wash everything on cold (my cold water is about 65°), and use the shortest cycle.

Minimal drying time at low temp.

The only time I separate is when there’s something new - that will get washed once by itself or with like colors to ensure the dye is set. And I avoid washing reds with whites.

I separate by the kind of detergent and cycle a thing is run on.

Gym/sleep t-shirts, denim, towels all get a hot wash with oxi-clean and fabric softener because I love the smell come at me bro.

Elastics - things that are mostly elastic/spandex/polyester - socks, underwear, leggings, sports bras. They get a hot/cold wash with a pre soak and extra rinse. The they get the free and clear detergent that washes cleanest and leaves no smell.

Daily wear/delicates - gentle cold wash with woolite with low tumble dry or hang dry. I only ever have like 4 of these with each wash. Generally the nice, more expensive stuff I wear in public that I want to last a long time.

I don’t care what color anything is.