Thanks a bunch everyone! The comments have been helpful. From what I have researched it probably isn't HUGELY important to have mega R value on the floor, as I think only about 15% of ALL heat loss goes down, also b/c at 8 or 9 feet below grade it isn't all that cold anyway. It probably just FEELS colder as concrete conducts heat away. I'll probably just try to get the heaviest non-organic pad that I can and throw the carpet on top of it and it will probably be fine.