So I can understand the wish, since we are planning exactly that after we experienced it that way on a vacation!
But a window for ventilation and natural light is mandatory in my opinion.
We are also planning about 1m width and 1.2m length, a sliding door between a closet and the toilet.
And we think a sliding door is definitely better than nothing, and still it’s not an extra room if you need to quickly jump between the shower and the toilet. And even through a wall you don’t have 100% soundproofing. So absolute TMI but after all, you live together as a family.
Find a better position so that you can also use the wall for a shelf outside or next to the shower, for example
(-> and just now there is exactly such a suggestion as I submitted)