I sleep under a duvet every night.
I find it difficult to sleep without one no matter how warm the room is, it just feels wrong..
The house I share with my friends has a habit of bleeding heat like no tomorrow, so it's a necessity!
It's insane, you turn the heating on - the house gets really warm, you turn it off and within an hour it's FREEZING.
Fortunately my radiator is right next to my computer chair.