Heat pump misplanning, currently heating with an instantaneous water heater

I built my first single-family house 5 years ago in the NRW area, Dortmund. It has a living area of 170 sqm + cellar room + attic (not developed). At that time, a completely normal boiler was supposed to be installed, but the heating company persuaded me to install a geothermal heat pump system. The advantages convinced me back then, so I agreed to the extra expenses, among other things. I also didn’t have to have a gas line laid from the street, so I would save something there J. So the extra expenses would be worth it. At that time, he calculated that I would manage with a 6 KW stove, and accordingly I commissioned the drilling company to carry out a borehole. This was drilled to a depth of 95 meters (costs about €4,500) according to calculation. The electrical work, including an extra meter from the municipal utilities, was also completed. After that, the heating company had to close for personal reasons. The company that recommended this system was therefore no longer there. I was left empty-handed because at that time I couldn’t find a company that wanted to complete the system with the borehole. They all said that the 6 kW system would not be sufficient and that for a larger system the 95 meter borehole would not be enough. So I was supposed to have a second borehole done, and if the company was to come, I would have to pay another approx. €4,500. Since everything except the heating was finished by then, and we had to move out of the old house, we decided to move in as quickly as possible and heat with a normal wood stove (we had the chimney shaft built during construction). Since then, we have heated the hot water with a tankless water heater. Financially, we also had no reserves, as there are always unforeseen expenses when building a new house. Since then, we have been heating our apartment with the wood stove; when it is sometimes not sufficient for the children's rooms, we heat them with electric heaters. Now that we have somewhat recovered from the house construction J, we want to complete our system. What can you recommend to me? Can anyone recommend an inexpensive alternative, what can be done with the situation? Would I receive funding in this condition? PS: The house has underfloor heating on the ground floor and radiators on the upper floor.

They all said the 6 kW system would not be sufficient and that for larger systems the 95 meter borehole would not be enough.

People usually say a lot when something is to be sold! ;-)

... So I should have a second borehole drilled, and since the company was supposed to come, I would have to pay about €4,500 again.

Nonsense without calculation (proof)!

... and we decided to heat with a regular wood stove (we had a chimney shaft installed during construction). Since then we have heated the hot water using an instantaneous water heater....Since then we have been heating our apartment with a wood stove; if sometimes it is not enough for the children's rooms, we heat them with an electric stove.

An expensive "pleasure" in the long run!

... Now that we have somewhat recovered from the house construction, we would like to complete our system. What can you recommend to me?

First have the output and energy demand for heating and hot water calculated.

... The house has underfloor heating on the ground floor and radiators upstairs.

Also check (have recalculated) whether the heating surfaces and hydraulics are even "heat pump suitable." Changes will probably be necessary upstairs.