Are you saying the toilet is in it's own room with a door? If it is, I wouldn't add a door, Here in the western part of the US, you very seldom see a door on a master bathroom. If you do need a door though, it might be a good idea to square up the doorway and use a French door with obscured glass. Just my opinion.

BTW, I wouldn't install a barn door. It's one of those things you'll regret years later because it's a fad item. Again, just my opinion. I'm a realtor

Thanks for the thought! We weren't necessarily into the Barn door idea, but it seemed to be the simplest solution for an arched doorway. We just want some privacy to the toilet. It's currently in a separate room (entry to the right in the bathroom), but no door. Is it costly to square up the door way?

I design complete homes and space planning for remodeling project as well as interior design for a living in the Chicago area and the first thing I ask my clients is how they live in the space. Do both people sharing the space get up in the morning at the same time? Lighting and noise become a consideration when one person is still sleeping and the other is getting ready or even when someone has to use the bathroom in the middle of the night. Is privacy an issue? I personally want the option to close a door when someone is using the bathroom, for their sake as well as mine. Additionally, it also appears that if you don't close the curtains in the bedroom you could be exposed to the neighbors as well. Putting any kind of door on a curved opening is going to come with a cost, just depend on how you want it to operate and how much you want to spend. It looks like the opening into the bedroom has a wide jamb which allows you to put a single swing door. if you don't want the expense of customizing a curved door, you could square off the top portion either with drywall or a curves wood panel or transom to go over the door. Be sure to consider whether or not a glass door is right for you, light from the bath will still be an issue if you do glass even if it is frosted and it does not give the same noise control as a wood door. The surface mounted sliding door will be the least invasive and can be changed later is you tire of it. If you have enough space, I would hang a single sliding door on the inside the bathroom, (watch out for light switches and HVAC interference). You may need to consider the door relationship and the chair rail. Either the door can be set out enough to clear the rail or you may need to remove the rail in that section and replace is with something flat that reflect a similar look of that detail when the door is closed.

You'll have to ask yourself if putting a door on the bathroom entry provides enough privacy to solve the toilet issue (?) Unless you know for sure you want a door there too, I would advise starting with the entry door first.

Good luck and hope you post a picture when you have it completed!

If it were me, and you don't have different waking and showering times, I would just add a door to the toilet room. It would be the most economical fix and you would be able to keep that beautiful arched opening. It's a great feature and makes your bedroom seem more spacious and interesting. To square up that doorway, you would need a framer, dry wall installer, door hanger and painter. As you can see, it could add up quickly. Best of luck to you.