The reason basement floors feel cold is that concrete is a good conductor of heat, it is like walking on stone that is cooled to about 55 to 60 degrees (depending on geographic location)
But, 55 to 60 degrees is not a lot of temperature difference from the 68 to 72 degrees you want to keep the room at, therefore you don't need a lot of insulation value to make the floor feel comfortable.
What I would do is install carpeting with a 5/8 inch thick carpet pad. The insulating value of this combination should be adequate.
This assumes, of course, that you don't have any moisture or water problems in the basement.