If the baseboards are hot-water radiator, most people would say that's better than forced air--more consistent heat and no draftiness/blowing. Quieter too.

I don't know geothermal, but I would think that it would work really well with hot-water radiators, since all you need is a heat exchanger for the water.

The biggest hurdle in converting to forced air would be, do you have the space to run ducts up thru the first floor to the second floor. Then, How can you distribute the air to each room on the second floor, will you tear up floors or tear up ceilings below?

I agree that baseboard heat is optimal, especially if the baseboards are hot water radiators. They are highly efficient and provide consistent heat. Retrofitting ductwork for central AC involves a lot of idiosyncratic technical issues. You will need a competent contractor to look over the place and give you an opinion on how-to and the cost.