I use kijiji, even with the dwindled userbase compared to marketplace, signal instead of messenger, and I wasn’t going to events anyway, so I’m set without facebook

I would refer to that as thickness, but I’m not a jeweller. My advice stays the same though, try some on and see what you like.

My wedding band is ~8 mm and i’ve never worn a ring less than 4 at its narrowest point. I would say just find something you like the look of, and see if you can find something at a jeweller that’s similar you can try on if you’re that worried about the fit.