For hot sleepers, this can be immensely difficult to get right. I struggled with insomnia for months in part due to the fact that temperature fluctuated as the convecs heater sucks. Best results were to keep the room cool enough that I could sleep with a sheet and light comforter. Having the comforter "partially" covering when I felt hot doesn't work. Layering sheets doesn't work either, as by the time you've piled enough, it traps too much heat which doesn't escape.

I tell you, it's all such a head ache.