Don't wear cotton! Cotton kills by keeping you wet and stealing your body heat! Poly- pro is your best bet.
If you are getting really cold at night and you need some heat try using an emergency blanket or bag (you can get them almost anywhere in a camping section). The crinckly sound can be a bit loud and feels a bit strange inside the bag but you'll be toasty warm in almost no time at all. It's also handy if you don't have alot of extra space in a sleeping bag for extra layers of clothes.
Another thing you can try is wearing a hat to bed. You lose an amazing amount of heat through the head.
If I go to bed cold I make an extra effort not to ignore it. If I don't stay warm I wake up tired because my body hasn't really rested. It's spent the whole night trying to keep me warm.