Wrapping the bathroom is pointless. In controlled residential ventilation, this is an exhaust air room.
Sorry for the digression, but the still immature plan to insulate the interior walls is not entirely pointless. With the same heating surface and supply temperature, the bathroom will be warmer if you insulate it slightly from the colder rooms.
Instead of a 40cm thick interior wall, a few centimeters of additional insulation will surely suffice. But all of this should be calculated in advance when planning the underfloor heating.
Controlled residential ventilation has little impact; exhaust air rooms receive warmer air than supply air rooms.
18° in the bedroom and 24° in the bathroom are hardly achievable without insulation between the rooms, for example. Furthermore, the efficiency of the heat pump decreases significantly if you have to operate it at a higher supply temperature for the entire house just because of the tropical bathroom.
If
permanently high temperatures are needed in the bathroom, you either have to accept permanently higher electricity costs or plan accordingly in advance: lay underfloor heating into the walls and, if necessary, insulate the interior walls slightly. Especially towards the bedroom.
We planned our bathroom at only 21°, did without wall heating and insulation, and installed an additional electric heater to be able to heat electrically
when needed. But it may not be allowed in Austria, no idea.
: I would especially plan the underfloor heating for the bedroom, if you do not insulate the wall to the bathroom, with a loop so that the dressing room is fully covered (warm) first, and then the pipe is laid further into the actual bedroom (cold end). That will (slightly) support the bathroom and costs nothing.