Heating solution for attic conversion

Hello everyone,

I am looking for a suitable heating solution for the conversion of my attic. Here are the key details:

- End-terrace house, built in 1998, 10cm external wall insulation
- The attic is currently not developed and will get dormer windows on both roof sides and will then be divided into 2 rooms, each approx. 20sqm per room
- The two rooms in the attic will be children’s/teen rooms, meaning they will be used intensively for many years – and thus heated –
- Roof insulation: 16cm mineral wool between rafters, 14cm wood fiber insulation on roof
- Heating: gas central heating (built in 1998) with buffer tank in the basement; ground floor and 1st floor are heated via radiators (no underfloor heating); additionally a wood stove on the ground floor; despite its age, the heating system is in top condition and very energy-efficient
- My currently preferred solution for heating the attic: hydronic underfloor heating connected to the central heating/buffer tank in the basement; problem: neither a heating circuit nor empty conduits etc. currently run to the attic; a breakthrough through 3 ceilings (basement ceiling, ground floor ceiling, 1st floor ceiling) would be necessary, which I would prefer to avoid.

Does anyone have ideas or tips for
... a simple solution on how I could still realize my hydronic underfloor heating?
OR
... alternative heating concepts?

Best regards
Matthias

My plan A would be an extension by one floor with radiators, and therefore no additional circuit from the basement upstairs. Plan B would be an additional split air conditioning system to be able to cool in midsummer and heat in winter (with [Photovoltaik] support?)