Usually just underwear. I may wear a pair of pyjama bottoms to bed, but 9 times out of 10th I will take it off in bed because either it twists and rubs, or just the feel between the fabric, my cotton throw and the bedsheet is too uncomfortable. It's not often a case that I get too hot, just rather I find it too awkward.
I also never really wear socks in bed either. Once in a blue moon I will because I've been too tired to take them off or have fallen asleep before I've realised how uncomfortable they are.