Rugs, Carpets and Carpeting - What carpet and carpet cushion over garage?

We have a typical case of a bedroom over a garage in a house built in 1968. We do not want the expense of increasing the insulation in the garage ceiling. However, the carpet in the bedroom has to be replaced; we know the carpet cushion has disintegrated. What combination of carpet and carpet cushion will do the best thermal insulating? Also, is it possible to even put something under the carpet cushion that is firm and has insulating properties and that will not contradict the capet manufacturers recommendations for carpet cushion thickness?

There are foil-backed thermal insulation products available to go under carpet. There are also radiant heating products available. Carpet offers insulative value. Carpeting constructed with a deep, dense pile and a thick, densely air-pocketed urethane carpet padding tends to offer good insulation.