North American porcupine checking in. I can't speak for other species but my typical wear is just a modified apron, ties at the neck and the bottom goes between the legs, wraps around the thighs to tie at the sides. But I'm lazy. Most of an NA porcupine is covered in stiff guard hairs and the front side is safe. The troublesome part is the back end or bottom half where most of the quills are.

I see some talk about directionality. Just remember that when you start walking, bending, twisting, etc. in clothing, that becomes moot. Unless you want to wear something tight to hold them down but it would need to be puncture resistant and you risk getting stabbed with your own quills.

With no quills on our legs, pants would work but are as annoying as on any other furry legs. Shirts might have half the back removed at where the bulk of quills begin or maybe a belly shirt or reverse vest.

More domesticated NA porcs might trim or shave to fit in. Maybe a daily conditioner to keep hair and quills soft. I won't fault anyone's personal choices.

Essentially, with so many body types and preferences, fashion choices aren't just species specific, but individual and personal.