Floor construction with a maximum height of 6 cm with insulation

Hello dear forum,
I have the following problem with my recently purchased house (from the 60s). Due to moisture caused by a non-functioning vapor barrier, the floor structure in the basement, which is used as living space, had to be dismantled down to the floor slab. The old structure had a height of about 6 cm. We want to have a structure of a maximum of 6 cm again to avoid having to adjust numerous doors, steps, and transitions in terms of height. The costs would otherwise far exceed our budget.

Therefore, my question: Is there a reasonable floor structure that would also provide some insulation? Our carpenter recommends a structure with a vapor barrier, wood fiber insulation boards of the Pavatex brand, and wooden plank floors on top. This version would have the advantage that one can do without the screed, thus saving 4 cm in height and still have reasonable insulation.
Can anyone provide information on how these wood fiber insulation boards behave if the vapor barrier should allow some moisture through?
The craftsman from the construction company that did the dismantling painted horror scenarios with mold under the wooden floors.

Thanks in advance for your contributions.
Bumsi

How is that supposed to become stable? I don't understand.

If an Alujet Reflex or Katja Sprint were installed, then some PUR insulation and dry screed on top.

In the basement, presumably on a slope since there is a living room, I would primarily have concerns about moisture penetrating from below and in the area of the basement exterior wall's bearing point given the construction age. Is there any visible or known sealing there, and how was it resolved?

I would also suggest Jackodur/Wedi/whatever - cement-coated fiberglass-reinforced XPS board. The board does not care about moisture, the vapor barrier is integrated, it definitely does not draw moisture from below, and it also replaces the screed – provided the floor covering does not allow point loads. So multi-layer parquet, solid wood planks, or tiles are possible. Thus, bond 40-50 mm boards and lay the covering on top.

First of all, thanks for the ideas. Correct, the house is on a slope! There was virtually no sealing. The plan is actually to install paraffin barriers with floor transitions to the vapor barrier on all walls facing the ground so that nothing can come through from there anymore. Do I understand correctly that you would also forgo the welded vapor barrier with the XPS boards, or does that still have to be underneath? The construction of the Pavatex boards would be done with special joint battens. My biggest concern would be: if moisture ever gets into my floor for whatever reason, these eco boards would probably mold quite quickly. I understandably have little desire to tear everything out and put it back in again. I had forgotten another problem. The floor slab is pretty uneven. Would that still work with your versions?

Do I understand correctly that with the XPS boards you would also dispense with the welded vapor barrier, or does it still have to be underneath?

You no longer need a vapor barrier against moisture from the indoor air. However, I would still do the sealing against external moisture, because this can slowly enter through joints and the edge area.

What do you mean by uneven? The XPS boards are glued with adhesive mortar or construction adhesive. If the unevenness can be compensated this way, no problem. Otherwise, you need to use leveling compound beforehand. The boards should be fully glued over their entire surface. Leveling with perlite granulate is not possible, because the boards should not be laid floating if there is no screed on top. Also, the build-up height would then no longer fit.

Retroactive floor insulation in the basement or in areas without a basement is always critical regarding moisture. Because of the ground, the underside remains permanently cool, which reduces evaporation in summer (as with roofs or walls).

Wooden flooring on battens with a vapor barrier and insulation mats between the battens can work, but I would feel uneasy about it, even though I usually try to build as "naturally" as possible. Of course, it is also possible on uneven substrates.