I'm with S-F on this one. Sealing up the cracks and holes will give you the biggest bang for the buck. When we replaced our windows I found that they had been "sealed" with compressed fiberglass insulation. I could have done myself a lot of good by removing the trim, pulling out the insulation and foaming the windows ...
However, we too were on electric baseboards and we cut our bills by sealing all the windows with plastic. It's cheap and takes an afternoon. Our sliding glass doors from the family room got two layers. One inside and one outside the house. This is because the first wind storm from the north west pushed the inside layer into a balloon like shape and eventually broke the seal.
I added a pellet stove in the basement. That sucker saved us thousands of dollars. We had a wood stove but it was so messy. The pellet stove was cleaner and more manageable for us.
I also spray foamed and put gaskets around switches and plugs on the exterior walls. I also put new gaskets around all the doors.
Had I known about sill plate insulation I would have done that too. But I hadn't joined this site yet. There's a really good post on sill plate insulation. Maybe somebody else remembers who did it. Good luck.
