Seamless bathroom, is it feasible?

Have no experience with what was offered. However, do not consider it "optimal." We have seamless bathrooms. They were realized with the system from Dold. Definitely look for someone who has experience with something like that.

I am bringing one of my favorite products into the race again when it comes to a seamless look – also because of the diverse design possibilities: Brillux Mineralico (or similar) Although I can't currently find reliable evidence of suitability for use in the shower area, I also wouldn't know any reason against it.

...
Prices on the internet for walls are given at about €200 per m². Is that roughly the range one has to expect or did you pay?

Mineralico was once offered to us at that price.