Bauexperte and Yvonne, do you really think that a lot of light comes through the windows? These are 80x80 windows facing north.
Not much, but enough. We have a window 65H and 140W to the north in the bathroom, which is also enough for our 9 sqm. If you had a window without a parapet 80 wide in that position, the whole front half would remain dark.
I also like Yvonne’s idea of swapping the shower and tub from (my) variant 2; it could suit the room well; it would especially further ease the situation around the washbasin. Glass instead of masonry should also be the means of choice in this variant.
I would then possibly turn the toilet so that you don’t face the door, but look at the shower. I personally always find it nice to have the tub near the washbasin, as you have a place to sit by the washbasin. The towel holder can go to the left of the windows, opposite the door.
And everything is nicely separated.