If I had the opportunity to start from scratch with a house, and had reticulated gas, I would probably go for either a gas central heating system, an inslab underfloor heating system with a gas boiler or a radiator system.
There are califonts (i.e. infinity hot water) available which have a secondary side which can be used to heat water for radiators. The concept here is that you only have one piece of plant for heating domestic hot water and your radiators. Adds 25% ish + the cost of the radiators and pipework onto the cost of your instantaneous hot water system but also heats your house.
To me only heating the lounge is a waste of time. If you want a warm home you need to look at the whole floor plane and figure out how to efficiently heat the whole thing. We spend as much heating the bedrooms with oil column heaters as we do heating the lounge with a heatpump.