I did think about going down the heat pump route but basically we ran out of places on the outside walls we could put a system.

I know it probably seems contradictory, but I actually prefer our coal fired heating system... with the insulation we have, we need it for maybe three or four weeks out of the year, it has to get down below 4 degrees C outside to require it. Which happens rarely here, and is likely to get less common in the future. (and coal is *cheap* now.)

I suppose if wanted to go greener, I would upgrade our air-con to one that has a heater function, and use some of that solar power. Or you know, I could just burn wood instead.