Before I put an electric heater in, I would put an unvented natural/propane
gas heater in the coldest spot. (unless you have small rooms and closed
doors)
I have one in the kitchen/living room area and we use it when it is too warm
to start a fire in the woodstove.
Just make sure you put a Carbon monoxide detector in the room.
--
Joe

The problem too is that the house is cold on one end and warm on the other
in the winter. The easiest thing seems to be adding a electric heater to
help a bit.