A regular mattress is a natural insulator - no need for
blankets between it and your body. Plenty of internal
openings between the layers of padding and the
springs. sheet/blankets/comforter on top it is!

I on the other hand am so sensitive to drafts/temp
differential, if one foot is uncovered in bed, even in
JULY, I am positively shivering. So when changing
the sheets I make sure that end is super tucked in,
even if there's 6 inches less covers up at my head.