For winter camping ground insulation, most of the Scouts around here (Chicago burbs) go buy the foam construction insulation from Home Depot, cut it to size, then cut it up widthwise to decent folding chunks, and then duct tape the chunks back together so that it can fold in a Z-fashion. Then the "comfort" pad goes on top of that.

Yeah I agree that sleeping on a cot with lots of insulation sounds kinda odd. My vote would be to sleep on the ground with a Home Depot construction foam on the floor of the tent (as large as possible/convenient) and then a really thick self-inflating foam pad on top of that for comfort. DON'T use an air matress!!! I use the large size Cabelas Ultimate Self-Inflating Sleeping Pad. Its 3.5" think and WONDERFUL!!! Not cheap, but wonderful!!