I had a heat pump installed in house that was very drafty on two sides, with the third side being a party wall (so the opposite of drafty) and the four uninsulated masonry in open air. Maybe 20 days per year when temp dropped below 26 and 60 when it dropped below freezing. It performed beautifully. Of course, there are lots of other factors like how fancy you go with the hardware; ducting; air handler and the like. Ours was middle-of-the-road and we didn’t add insulation or make any major repairs or additions. In the US, companies will give you a free estimate or low-cost estimate of how many kilowatts of energy it’ll take to heat your place with a given setup. Ours matched very closely the estimate.
Good to know! How is the heating system set up? Radiators or minisplits?