Personally, I have trouble falling asleep without at least a light bed sheet.

I'll sleep with a very light sheet up to around 25c.

I keep my house at around 22c during the Winter. I'll match a light sheet with a light blanket at that point as it gets chillier randomly during the season.

I dislike air currents flowing across my skin while I'm trying to sleep, unless it's crazy hot (the central air system moving air around is enough to annoy me while I'm trying to sleep, without a cover).

A thin sheet sometimes, yes. Mostly for comfort though, as I can go without.

I do. When I fall asleep in front of the TV (my bedroom is normally colder) without a blanket I wake up freezing. Even in summer nights I prefer a very light blanket to cover myself.

> 40°C , still sleep under a cover