I am in the same boat with the cement slab right beneath the carpet pad and carpet. I too am paying very high heating bills. I have no idea what product to use but I know what is missing or should have been applied originally. I also have the freezing air space between the first floor ceiling and second floor that has no insulation in the area. My reply to post "slab insulation" goes into more detail of my insulation issues.
Thank you for yout time and help, you will never know how much getting some help means to so many of us.