Which flooring is suitable for underfloor heating?

In the upper floor and attic we don’t have large windows facing south.

In the upper floor there are only 2 normal windows facing southwest and in the attic there is only the roof window facing northeast and 2 floor-to-ceiling windows facing north.

We don’t have the problem with great heat due to sunlight.

Well, then the problem would already be solved.

And how about the room layout? Floating installation cannot cover large areas continuously, otherwise the tension becomes too great. This often leads to having some kind of track installed as a transition at every room door. Not really nice. With glue-down installation, this is not a problem at all. In our house there is an east-west axis measuring almost 17 meters. Along the entire stretch there is only one room door, which is almost always open. Continuous installation with glued vinyl is no problem here.

Rigid (or SBC) vinyl can be installed floating continuously over an area of up to 400 sqm. No transition strips at door thresholds needed. In case of damage, the affected area can be quickly repaired or replaced without having to "tear" the planks from the floor. Rigid is also not as susceptible to direct sunlight as described here.

Thanks for your message.

our rooms are:

approx. 11 sqm, 13 sqm, 16 sqm and in the attic approx. 36 sqm

Your recommendation is rigid vinyl?

with the types of vinyl, as a layman, it’s hardly possible to keep track anymore

Yes, Rigid Vinyl, also called SBC Vinyl. Relatives have installed it floating in their house. Admittedly, only for 3 years, but no problems since then. The sun beats down on it for half the day. We will lay ours in 4 weeks, continuously in the open-plan area on 45 sqm and on the ground floor on 60 sqm.
A very small disadvantage: compared to normal vinyl, rigid vinyl is quite heavy (due to the hard core). That is not an advantage during transport.
Whether this is the ideal choice... no idea. We decided on it.

How will you install the Rigid Vinyl?

Will you put an impact sound insulation layer under the vinyl? The Rigid Vinyl already contains the impact sound insulation.

Or will you simply lay the Rigid Vinyl on the floating screed?

The relatives installed it without impact sound insulation because, as you correctly say, it is already integrated. My buddies from the upholstery next door said that you can do it that way if the floor is absolutely level and clean (for example, with newly laid screed). Otherwise, the mat also helps to even out various unevenness and allows the rigid boards to "float" better. We will probably lay the mat recommended by the manufacturer underneath. But as I said: there is simply no long-term experience with the rigid yet. In the end, there might still be a catch that cannot be foreseen now.