Bumping into a companion NPC lets you sort their armor with a press of r. However you can also have them UNEQUIP items via this menu as well. So that means you talk to an NPC, tell them to use an article of clothing via g, sort em’ with r and kit them out as you please. If their armor starts to get ratty just strip em’ down and repair it.
Personally I prefer to go the route of kevlar reinforced gambersons for my companions, as they’re not very labor intensive.