I’m sympathetic to the desire to mitigate the drawbacks of mutations somewhat, but they are intended to be drawbacks, so we’re talking about mitigation here, not removing all penalties for them.
Any solution for “mutation-fit” clothing needs to be relatively simple. An example would be a “mutation fit” flag, and a corresponding “minor” version of the mutation flag that makes a mutation incompatable with clothing. The main problem with that is the flag would necessarally reduce effectiveness of clothing as well, which either requires a ton of special case code, or the stats being pretty non-representative most of the time. also we could tag some clothes “mutation-friendly” by default, like with a wrap or turban, etc. The problem there is that wouldn’t apply to pretty much any armor, just clothes.
Frankly I don’t have a good and simple system to do this, in addition to a rationale for it, you need a way for it to work.
Some stuff, like webbed hands, curled horns, antlers, just aren’t going to be compatable with most clothes.