to avoid losing your body heat to the cold ground, why not lay down a space blanket between your tent and the ground?

i would imagine that it would reflect any body heat back up to you instead of the ground. of course, it might make some noise. but it would probably be quieter than if you put one over top of you.

you could also try cutting off two small pieces of the space blanket, and placing them inside your cycling shoes as to cover the holes for your cleats. you don't want to lose any warmth through there.