Another issue with crawl spaces is the potential for Radon problems.  I would go with either a full basement with infloor heat or a well designed and planned out slab with infloor heat. Forget the crawl space, imho.  My basement has infloor heat with porcelain tile over it. Very nice and easy to clean. Use rugs where you want some softness. Warm porcelain tile feels great to the feet. Tile conducts heat well. Good luck.