If you have to lay on cold concrete or ground to work try getting a one inch thick 4x8 sheet of styrofoam. It will insulate you from the cold surface.

 

I have a roll of carpet padding that I can double up, and lay on. (and not get killed for having oil dripping on it. )

Learned that trick sleeping on the ground out in the desert..... Yes, I learned, because I screwed up, and insulated myself from the AIR...... ground absorbs heat one hell of a lot more efficiently than air..... Took a sore back to learn that one.