Fitting a larger shower in the floor plan - Which size to choose?

Thank you, Alex! That sounds good. That will probably fit in my bathroom.

If I want to build a wall on one side of the shower, how thick would such a wall be approximately? The wall is not ceiling-high, but up to 200cm. Glass blocks are 8cm thick.

As a rule, you should be able to build something like that with an 11.5 cm block, you might also be able to use an 8 cm aerated concrete block, the important thing is that the wall is well anchored in the wall. In addition, there is putty, possibly plaster, and of course the tiles. So I would definitely expect 10-13 cm.

We have the 1.20m in width.

In the house, we are now planning 120x90

oh, 13 cm would be a problem, 10 cm would still work. Maybe glass blocks after all? Would they create a fully functional shower wall?

I have planned an 80x100 shower, where 100cm is the width and 80 the depth. I believe I mainly need space in width and not so much forward.

That doesn't depend only on the entry side, but also on the side where the mixer tap is installed. The larger dimension, where their space requirement isn't deducted, makes less sense. In the floor area, 80/100 is equivalent to 90/90.

Glass blocks are 8cm thick

They actually come in different sizes, or do you mean specific ones that are already planned in this building?
I wouldn't use them because of the joints.
My favorite would be to ask if it can't simply be built with pre-wall constructions (for the flush tank installation, etc.). That could result in a finished size of 10 cm, i.e., half the width of a 20 cm tile.

The bathroom is quite small (220 x 180).

Have you considered a cabin with a rounded corner?
Depending on the surroundings, that might fit more conveniently...

Glass blocks were just an idea: they let some light through so that I’m not standing in the dark in the shower. The planned wall separates the shower from the washbasin, which is located on the other side of the wall. I would prefer not to plan the room length larger than 180. I am calculating 90cm for the washbasin, 80cm for the shower, and 10cm for the shower wall. A glass partition would of course also be possible, but I imagine it would be awkward because the washbasin is directly adjacent to it. If I use a shower wall, it has joints just like a glass block wall, doesn’t it? Or is it about the number of joints? The tiles are after all twice as large as the glass blocks.