Simply install an air conditioner and you will have very efficient room heating (no hot water, though). They cost about 1500€ and are really easy to install. I know in Bulgaria many households have switched from oil heating to air conditioners.
That's not that easy with German homes as they are heated with hot water pipes and walls are typically solid. You could maybe install a device that emits hot air in a single room, but to install a forced air system, you'd need to in essence remodel the entire home. In addition, you'd have worse outcomes because now the nice warm floors are gone.
In that case you need to install air/water heat pump, which not only heats the house but also the potable water. They're more costly than regular heat pumps, but are _better_ choice than individual heat pump units around the house.
It's a more difficult situation if the house lacks water circulation (heated floors/radiators).
Why an air/water heat pump and not just a water heat pump? AFAIk heat pumps are becoming quite popular in Germany in recent years and are definitely a very viable option unlike "air conditioning".
I did just that to my house in France. Everybody here (south east of France) does that. Seen the savings and that it both cools in the summer and warms in the summer, it's a complete no-brainer. In addition to that I switched my open fireplace to an enclosed one: the efficiency when burning wood is greatly increased. And I stockpiled on wood. So should there be electricity shortage preventing me from using HVAC to warm the house, at least nobody is going to prevent me from putting wood in the fireplace.
In some places it is actually illegal to install an AC at home. For example in Switzerland. Unsure about Germany.