Base slab in water -> Alternatives to WU concrete?

Hello and good good day!
I am new to the forum and signed up because I have a question about our construction project:

We are building a single-family house in the Südheide. Timber frame construction, 1 1/2 stories, 170 m² living space.
The soil survey showed that the groundwater in the built-up area stands at 1.2 to 1.0 m. A borehole next to the built-up area showed 0.9 m. On top of the topsoil follows fluviatile sand, gray --> medium sand, fine sandy, slightly coarse sandy.

Originally, a slab with frost skirt was planned (thermal foundation slab with PE foil against ground moisture). After the geologist and the architect had another conversation, I was advised to invest in a slab made of WU concrete. It would - since in the worst case a groundwater level several decimeters higher is to be expected - mean that the foundation stands in water. Therefore WU concrete. +10 cm higher slab, the cost is over + 8,000€.

The additional costs add up (obviously) and I would like - if possible - further assessments on the topic.

My first question:
What are your experiences? Is the slab actually threatened to stand in water, or is the geologist being too cautious?

Second question:
If the concern that the slab could temporarily lie in water is correct, are there reasonable alternatives to a WU concrete slab?
Of course, I am willing to do and spend what is technically necessary to protect my values in the long term. But I am curious for input.

Many thanks and have a nice weekend everyone!

Regards
Sebastian

I do not find that too cautious. We still have drought in the Südheide. Entire lakes have dried up here. If that normalizes again, the groundwater level will surely be higher!

...so at Lake Constance people have already had experience with pile dwellings

I'm not an expert, but I think you don't have many options. If you find anyone at all who will build it differently for you, they will surely not take any liability in case water ingress occurs. And honestly?
It might be that nothing ever happens, but with all the extreme weather conditions, maybe next year the water will already be that high, do you really want to ask yourself then why you skimped on the measure recommended by the expert?

I obviously see it the same way, see my last paragraph. Savings are only made at this point if it does not affect stability, durability, and warranty in any way.

Are there alternatives to the chosen WU floor slab?

Thanks and regards