I've never slept on a cot while camping but I do use an air mattress every time, my tired old bones need the cushioning.
A few years ago while camping in PA during Oct (tent camping) it went down to high 30's over night. I almost froze. Actually woke up shivering. I had mistakenly packed only 2 of my summer sleeping bags. I had one under me and one over me with a wool blanket over the sleeping bag. 2nd night in the ten with same temps I put woll blanket ontop of air mattress, sleeping bag on that and had only the other sleeping bag on top of me. I slept like a rock.
Lessons learned:
1) make sure to take proper sleeping bags
2) have twice as much under me as on top of me