I'm really not sure if the additional investment in a heat pump vs. gas will ever pay off. Which parameters are being used for calculations, no one knows what gas or electricity will cost in the future....
Especially since the better a house is insulated, the more "irrelevant" the heating technology becomes – because with very low heating costs, you can save a lot in percentage terms from my point of view, but absolutely nothing comes of it. Apart from that, gas is not available everywhere. For the environment, heat pumps (preferably geothermal) and solar power are probably the best.