Re: Limestone floor....what to do for warmth?
The problem is from the concrete slab and limestone covering are a heat sink.
They transfer the heat in the room toward the cold ground. Even though you have heat vents in this area ( which are probably located up high to begin with ) the lower level of the room will always be cold.
A couple of suggestions ......
1 ) lay 3/4 rigid foam down -- frame out a floor structure using 2x4 's as joists -- fill the bays with batt insulation -- glue and screw 3/4 inch tongue & groove plywood -- and you will have a far warmer floor. However, if the heat vents are up too high you will still feel somewhat chilly because the warm air isnn't coming from floor level --- but -- it will be a lot better than what you have.
2 ) similar to above except you could add hot water radiant floor heat.
Electric radiant floor heat is available but it could be expensive to operate for such a large area. These electric floor systems are great for a smaller area like a bathroom.
"" an ounce of perception -- a pound of obscure "