I believe that with the information known so far, it is difficult to give you concrete advice. Energy consumption very often depends on the respective users. In my house, once lived a person who had heating costs on 90sqm that were twice as high as ours on 170sqm. She had terrible heat in her place; the most extreme was a radiator in the bathroom; she then had a dispute with the reading company, but in the end, it was proven to her that she simply always turned it up to the maximum. My house was built back in 1990; back then, energy consumption was not given much attention, such astronomical consumption was not common at that time. I think you should inquire in detail; maybe another heating retrofit besides underfloor heating would be sensible for you. Today, modern houses are also heated with air heat pumps or fireplaces plus auxiliary heating, etc. If the house is otherwise properly built, it should still be possible to heat it adequately today. You say it is not a bargain... so maybe you are putting yourself under pressure. I would then think about that carefully. General statements from your acquaintances with some numbers won’t help you further. I am sitting here (finally) with a small flame in the rabbit stove, and that’s enough. Maybe the fireplace or a chimney system can take on the main role of heating? Further information would therefore be interesting, and I would get a professional to advise me on this matter.