Keep the high-pressure system and have a repairman add a few more vents or introduce restrictors where necessary to improve comfort by balancing the system. The smaller ducts are more efficient in heat transfer than larger ducts with larger surfaces and the high air velocities keep the ducts cleaner.
Actually, electric heat is almost 100 percent efficient. A heat pump would require you to change the entire duct system, so the cost of reinstallation would negate savings over a long time. Comfort would never compare to a good furnace or boiler system.
Keep the existing ductwork and cooling coil. Propane in most areas costs as much as electric heat; but it gives the option of adding a hot water coil into the high-pressure system, then adding baseboard where desired or even radiant heat and hot water - all from a boiler that can mount on a wall or in a small location.
If oil is avalable, the costs of heat can be cut in half.