I’m not a huge fan of cases but when I do use one it has to be minimal. I’ve used the iPhone X both naked and in an Apple silicone case but I’ve found one that might suit all of your minimal lovers.
I’m talking about the Tozo PP Ultra Thin. It’s only .35mm thick and covers the entire phone, leaving small openings for the ports. What I like about it is that it obviously adds very little bulk but adds grip. It also adds some plastic around the camera bump so adds some protection to the camera glass, although being sapphire it’s going to be hard to scratch the glass anyway.
I find the glass back of the X to be pretty grippy anyway but it’s the sides that I find slippery.
Drop protection should be fine for the back and sides stopping dings but (like any case) drop it face down and you’ll break the front glass. I still recommend Apple Care + to everyone with an X given the cost to repair.
One major downside is though if you want to take it off again it can be tricky, I managed to break mine when I took it off but if you are careful it’ll be fine.
