Underfloor heating / Wall heating / Ceiling heating - Alternatives?

So what you need is a heating load calculation. And room by room. This can determine how many watts each room requires.

You currently have great conditions. You want to insulate indoors anyway. This can normally be problematic in terms of mold. Now I’ll tell you a not-so-secret tip: look into wall heating!
This is a floor heating system on the wall.
Advantages: the screed stays, it is applied on the wall insulation, goes into drywall, can be done yourself, and is laid from one pipe per heating circuit (no solder joints or similar).

You will reduce the heating load anyway through insulation. A new glazing is also highly cost-effective if the frames are still good. A complete replacement is then unnecessary.
Also look into insulating the roof. It works just like insulating the basement ceiling with a low investment in DIY.
Even small thermal bridges like the attic stairs and roller shutter box can be done really well by yourself.

Once you have your heating load after the measures, have the wall heating designed accordingly. And at the lowest possible flow temperature. Then you are also prepared if a heat pump should come later.

Additional question: does the garden need to be redesigned or should it stay as it is? And how big is the property?

Do you have an average oil consumption from recent years?

Yes, I have it in the offer, I was just so unsure because my colleague's father-in-law is so vehemently against it and also acquaintances have just moved and are glad to finally no longer have underfloor heating (they had swollen feet, etc.) hence my question, not wanting us to have something expensive installed. When there were such great other options (so I thought it better to ask beforehand)...

So what you need is a heating load calculation. Room by room. This allows you to determine how many watts each room requires.

You currently have great conditions. You want to insulate inside anyway. This can usually become problematic regarding mold. Now I'll tell you a not-so-secret tip: look into wall heating!
That is underfloor heating on the wall.
Advantages: the screed remains, it is installed on the wall insulation, fits into drywall, can be done yourself, is laid from one pipe per heating circuit (no solder joints or similar).

You already reduce the heating load through insulation. New glazing is also very cost-effective if the frames are still good. A complete replacement is then unnecessary.
Also look into insulating the roof. It works just like insulating the basement ceiling with a low investment in DIY.
Even small thermal bridges like the attic stairs and roller shutter box can be easily done yourself.

Once you have your heating load after the measures, you have the wall heating designed accordingly. And at as low a supply temperature as possible. Then you are also prepared if a heat pump should ever be installed.

One more question: does the garden need to be redesigned or should it remain as it is? And how big is the plot?

Do you have an average oil consumption from recent years?

Wall heating yes, I am aware of it but haven't really looked into it yet or it was mentioned once as an alternative to the panels, roof is completely new with warranty until 2020, we won't touch that (flat roof). The stairs only go to the basement (it's a bungalow).
The garden is about 80-90 sqm, it's an atrium, so anything that has to go into the garden must be lifted over or through the house, it can/has to stay as it is for now.

Yes, okay, if the roof is new, it was surely insulated at the same time. Then inform yourself about that. Especially since you want to do interior insulation anyway, these are ideal conditions.

The thick feet result from old times. Nothing was insulated here yet, bad windows, etc. As a result, the underfloor heating had to be operated with a high flow temperature. That caused the "thick feet." Properly designed and well installed, you don't even notice the underfloor heating anymore.

Oh, you can also install a ceiling heating system. But the wall heating is really suitable for you because of the already desired insulation. By the way, I would insulate with PUR boards. They insulate very well compared to other materials.

oh yes I do not have an exact house-related average consumption because the owners did not occupy the property. According to the chimney sweep who takes care of the entire complex, the average consumption is between 3500-4000 L (depending on the house type and of course personal warmth preferences). Almost everyone still has the "old" windows or window frames installed. The kitchen and bedroom have to be replaced because structural changes will be made there. The rest is postponed to later.