Catenary arches are the best form for delivering the forces of gravity onto two points (when considered in 2 dimensions or as a cross section of a catenary dome). To remember the term, I just realized that it is the mix of the three words "cat ate canary". I am thinking that a shallow inverted catenary dome made of a material with high tension strength could form the main strength of a floor system. A surface of concrete or similar structure would then take on compression strength and also provide thermal mass for a radiant floor heating system. The remaining space between the floor and the ceiling of the space below can be made of insulation (with compression strength to transfer floor weight to the catenary dome).