Can the 46cm gap/wall between bath and cupboard be removed? If so, move the bath up into that corner and then put the sink in the bottom right corner at the foot of the bath. Keep short heated towel rail below window and add another short one on the wall beside sink (at end of bath) - or add tall towel rail where sink is currently.

If you're thinking of sticking with a freestanding bath with no screen or curtain around the shower, you are still creating a wet room. If that's what you want and you have the budget for it, it could work - but as I mentioned earlier wet rooms are expensive as you have to tank the room (as far as I understand it). I also personally don't like them because a lot of the floor gets wet and there are splashes everywhere - more cleaning and it's difficult to get dry! Maybe I've only experienced badly designed ones though... The other option would be to have a normal bath (not freestanding) with a screen, or a freestanding one with a screen or curtain (if you google you'll see a few examples). You can get clawfoot rolltop baths which look freestanding on the visible side but are actually fitted against the wall so that you can have a shower above them.

Would it be possible to move the door so you could gave a shower tray on the 120cm wall? Then you'd have plenty of room for the toilet and basin/vanity on the 170cm wall.

If this will be a well used bathroom then you should visit a bathroom showroom and look at the size of shower baths and vanity units- when you know what you want in there you may conclude that you want to reduce the back bedroom size and make the bathroom a little larger