Retrofit bathtub or shower?

I think I'll just have 2-3 professionals come on site. Probably more sensible than any forum! Still, thanks.
Picture 2 mirror and shoe cabinet - that's where the shower or tub is planned

You are funny. You really can't do anything with the information provided.

You prefer to have 3 on-site appointments rather than a sketch?

I wouldn't show up for the on-site appointment without a floor plan. Or do you think the bathroom suppliers have nothing better to do?

Attached is the sketch. Toilets and sinks are marked in red.

The room in front is our spacious wardrobe. (Wall marked in black as well as door)
On the left wall we would like to have a shower or bathtub. It will probably be a bigger challenge since the hot water line is only installed at the sink! I am curious to see if the sketch will now help with good ideas?

I'm curious whether the sketch will help with good ideas now?

I've rarely seen such a carelessly thrown-together sketch. It doesn't help us. There are neither dimensions nor the place where you want to have the bathtub. Take a tape measure and please measure exactly where the existing bathroom furniture is and what the dimensions of the room and the additionally built wall are. Any deviations from the original plan are interesting.

It's more about the technical aspect: there is enough space, it is supposed to be in the room in front of the toilet and washbasin, not inside the room! That should remain as it is. Separate. That's why it was done that way.

Is there basically a basement under the room through which the pipes (supply lines, sewage) could be routed (regardless of the problem with the underfloor heating in the room)? Otherwise, you can completely redo the WC if you want to get to it.