Hi,
I also sew in my basement....love my sewing room! I do get some heat from the furnace in my room, my husband put in an extra vent as I am next to the furnace room, but in a MN winter it isn't enough...believe me! I have a small electric heater, bought it at WalMart, and I have it about 3-4 ft. from my sewing table blowing at me. I usually go down and turn it on half an hour before I plan on going down and it's just perfect down there. I also have a fleece shirt I keep on my sewing chair. I don't run it on high speed or temp, just enough to get the major chill out. Works well for me.
In the summer I close my two vents or I freeze from the central air. Spring and fall are great!
Bev