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.
.....and then duck