Actually oil heat is as inexpensive or less than other forms of heat now in cents per btuh. Your high heat bill would be even higher with other sources, like LP or electric. If you think you would save by adding a wood heater, then you need to consider the timn and expense of the new boiler installation and wood, either hours of labor or buying wood is expensive, unless you consider your time worthless. A part time job to make fuel bills is a lot easier.
The REAL alternative is to insulate the house, shut off rooms that are unused and expend less fuel.
Consider using a Kerosun direct-vented heater in the main areas that you occupy the most. You already have the fuel available.
Another VERY frugal choice is to move to a new well-insulated house with a better hot water oil-fired system which would cost less than one-third of the bills for century-old lack of insulation and wasteful steam heating systems.