I've got this on my to-do list as well. Did you already have the floor insulated? Sorry this is a bit off track....
My floor is 2x6 tongue-and-groove pine boards. There was no insulation beneath them (open to the crawl space) until I installed the styrofoam insulation. Once I get the woodstove going and the cabin up to temperature, the floors stay warmer than they did without the insulation. The bedroom is carpeted, which adds more insulation in there.