You should be able to do three panels in those windows up into that arch with horizontal louvers and fully functional. Your shutter maker just needs to line vertical posts up where you have vertical mullions! giving that center shutter something to hinge to. Here are a couple of similar windows I have done. It's a partial arch but it's the same concept with yours

Thanks team. Here's another idea - what about white wooden blinds? I actually like having no coverings on the windows for most of the time. eg. We have great views west and east, so the doors/windows are normally open 6 months of the year. They still need to be dressed, but with something that doesn't hinder the view. They could be up for most of the summer, and only let down if I need to keep some heat out or in winter to keep the cold out. I'm concerned they would be too heavy to operate being most of my window/door widths are 240cm. I've never worked with a consultant before... should I get someone to come in and give me a professional opinion?

Good luck wincymeow. I have a similar dilemma and it is not an easy one to solve without taking away from the "grand" look of a walk in shower. I am considering the extreme option of just removing the window and having tiles along that wall. The only other alternative I can see for you is to settle for the telephone box analogy (it did make me smile when you said that because I can see you think similarly to me in what you want to achieve) or to pay the expense of putting in a different type of window that sits high enough or narrow enough to not receive water splashes from the shower or to go with the option oklouise has suggested. I really hope it works out for you and you manage to achieve the dream ensuite you are hoping for.....( for my own sake, I almost feel like the more mental energy i put into the bathroom, the greater my expectation on its outcome and what i am hoping for, which is definitely not a good thing). Its a pity that you can't move any of the plumbing. I think if you are unable to make any changes to the window, then oklouise first suggestion is a good one - changing the orientation of the shower. (The only real negative with the layout that you have to stay with is that the door opening is in front of the toilet so it is the first thing you see, but I guess depending on whether you make the vanity area the feature or the tiles above the shower the feature, you can draw the eyes away from the toilet based on what you do. I think the changed orientation of the shower is a good compromise and depending on what vanity and feature tiles you use, the bathroom should look really nice because even your mirror will reflect the window and whatever is outside.

Curtains are coming back in at the local display homes and look very luxurious. Plantation shutters look stylish in the right house but I agree with the comments about the potential to look dated if not a good match for the overall house style. Rollers remind me of schooldays when the teacher set up the projector to show a film while the students struggled to get the blinds to stay down to darken the room, but modern rollers are a simple window covering which can be a good thing if all you want is something that opens and shuts in the background while other features of the room stand out. For something you'll really be happy with you need to be weighing up personal taste, house style, window style, functionality, maintenance, room usage, window orientation, etc. You can choose the trendiest look but if it's a nuisance to live with because it doesn't provide the required light/dark level or privacy or is noisy in the breeze or whatever, it is not the right choice for the purpose.