Wall construction:
Results in a U-value of about 0.3 W/m²K -> New buildings until 2020 had less than 0.24 as a specification for individual component consideration. Old existing buildings range between 1 and 1.5 -> a good value without need for action, also in the long term. Should something ever be changed, the inner lining can be dismantled and the insulation replaced with better insulating material.
Roof construction:
Also an energetically good construction here
Windows:
Triple glazing with double box windows. Not only energetically good, but also looks good. The U-value should be comparable with new windows without double boxes.
With this construction, I would expect that the floor slab or under the screed was also insulated accordingly thickly, especially since underfloor heating has already been installed.
For 95 m², I would estimate about 6000 kWh heating energy demand.
Z
for recalculation / rough estimation for advanced users:
Transmission heat losses:
Volume = 2.8m * 95m²
Surface/Volume = 0.8
Average U-value of the surface = 0.3 W/m²K
Transmission losses at U-value 1 = 75 kWh / m²a
2.8m * 95 m² * 0.8 * 0.3 W/m²K * 75 kWh / m²a = 4,788 kWh / a
Plus ventilation losses:
2000 heating degree days (rule of thumb including solar heat gains, moderate climate)
Air exchange rate of 0.3 / h
Air volume of 95m² * 2.8m
2000 K*d * 0.3 /h * 24h/d * 95m² * 2.8m * 1.2 kJ/m³K = 4596 MJ = 1277 kWh / a
Additionally, there is hot water with about 500 kWh / year and person
The underfloor heating will probably not be designed for 32/28, but for 40°C supply at design temperature - but it could also already be 35°C.
If you then install a similarly suitable underfloor heating upstairs, nothing would stand in the way of switching to a heat pump with a high annual performance factor.
So purely energetically considered, recommended without restrictions.