I'm a fan of mini-split heat pumps for their quiet efficiency & comfort, but I'm not sure if they'll work in this situation. There are ducted cassette mini-air-handler options for some amount of distribution between rooms, flush-mounted ceiling cassettes that fit between joists, floor mounted wall units (about the size & shape of a small wall-furnace or fin-tube convector) as well as the more common 12" x 12" x 40" wall-blobs.
The outdoor units are often wall-hung in multistory buildings but that's not always an option for aesthetic reasons. The refrigerant line max-lengths usually mean ground mounting pretty much stops at the third story.
Heating mode efficiency in a San Diego climate would have a comparable or even better operating cost than 83% efficiency natural gas furnaces.
They're not super cheap, but they ARE super comfortable, since the modulate and track the load for very stable room temps.