A secondary slot for each equipment slot that only affects the characters appearance and does not affect any stats. If no equipment is placed in the slot then the character's appearance will be that of the regular equipment slot. Perhaps add a crafting station that can convert any equipment into cosmetic equipment that has no stats and weighs nothing as well.
This is an interesting idea and relates to this post: https://playnightingale.ideas.aha.io/ideas/FEEDBACK-I-226
I am in agreement with one of the previous guests comments. As you would still need to craft a piece of clothing for it to be used in a cosmetic slot anyways, why not make it so all pieces that you come to posses can be useful in the later game. That way you could make the formal suit and top hat as equal to or better gear then the caveman clothes
Please no, cosmetic slots are unnecessary. Clothing choices should matter, they just also need to be competitive at late game materials wise. Cosmetic slots are a terrible pathway, just make clothing better in general so that all clothing styles can work. That way you NEVER need cosmetic slots, just craft the clothing you actually want to wear.