Can you insulate your basement walls? I did mine some 15 years ago, concrete made it easier than your stone, but what a difference it made. On the north side, I used to see the frost crystals on the cement. I powernailed 1 x 4's to the cement, then roofing nails to put up 1" thick hard pink insulation. You wouldn't believe the cold air coming in between the sill & cement either - The Great Stuff foam works good for that. Any insulation [even the stuff I used] has to be covered per code - They want sheetrock, solid paneling, etc. I used a fire retardant paint, about 50.00 for the gallon, but it was approved.