How many rooms in your house do you actually use? Can you close a few off during the coldest months? We used to close off the registers and then put rugs over them to help force the heat into the rooms we were living in. (At the time we were renting a 100 year old farmhouse -- lots of room but when the winter wind blew -- so did the curtains!)
I'm sure you've probably heard of the Scotch plastic stuff you tape up onto the windows then use your blow dryer to tighten it up. Looks almost like "glass" -- very clear and easy to see through. We used to use it all the time -- I assume they still make it.
What we ended up doing was getting a Wood stove -- and boy did it heat the house. With all of the excess rooms closed off -- We could keep the thermostat at like 55 or 60 and the wood stove kept the living room, dining room and kitchen plenty warm.
Good luck and here's to having a mild winter!