We have been using tarps, closed cell foam pads and our thermo-rests for years and this system performs fairly well. Short of buying a bulky and expensive insulated sleeping pad, I'm always looking for a less expensive, warm alternative. What about that old 30 degree down rectangle sleeping bag we all have in the basement? Why not use a light weight and very packable sleeping bag for a pad insulator?

I use the same system, thermarest on top of ccf. Sleeping on down would compress it so you lose the insulation value.

my favorite for winter camping has always been the Thermarest Ridge Rest closed cell pad.

I use an non insulated Big Agnes sleeping pad but I made a flannel slip cover for it. The flannel adds insulation and also makes the pad less slippery so my bag doesn't slide around all night.

I haven't tested it into really cold temps but down to maybe the high 20's I stayed plenty warm all night.

The flannel slip cover also packs up small enough that I can get it along with the folded up pad back into the original Big Agnes bag that came with the pad.