I had a cot that I used in all seasons. Great in the spring / summer / fall because of the air circulation underneath. Bad in the winter for the same reason.

During winter camping in New England (5 - 15º F), I tried using space blankets between the cot and bag. No help. A ThermaRest pad was better, but still chilly.

Some of our guys used air matresses and froze.

I finally used a strip of carpet and my ThermaRest on the ground and slept well.