I need top sheet, blanket, and quilt/comforter/duvet to be able to adjust to different temperatures. In winter I use all of it, in summer I just need a sheet and maybe the blanket. I can't sleep with nothing on me, but sometimes a duvet is way too warm.
I run into this issue a lot in European hotel rooms that only give a duvet. Waking up sweating and trying to figure out how many body parts I can poke out without feeling too exposed or too cold.