try to eat right before you go to bed; your body needs to generate heat during the night to keep you warm. If you wake up mid-night have a handful of trail mix etc. to keep the furnace going.

Also boil some water and put it in a water bottle and use to keep your core warm. It's worth it to put a bag around it in case of a slight leak.

Warmth is very subjective, that setup may be to hot for one person and freezing for another.