Can I add a furnace to my heat pump?

I had a radiator system that went bad last winter, I had it replaced with a heat pump because that's what all the different contractors recommended. Now this winter my heating bills are extremely high and I'm curious if I can easily add a gas furnace to my system. I already have the gas lines from the previous boiler. Can it be added to the air handler or would I need to replace my air handler with the furnace.