i'd do something bottom up/top down so you can have the top third open during the day.

Yes, that's my favorite. According blinds offer lots of options like that.

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So far the bottom up top down solution sounds best. I like this fabric look

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(if you go sheer you may need another solution for night time or your neighbors will be selling tickets to the show. a lot of louvers (even with mini blinds) don't close all the way... or as all the way as you'd like them too. make sure you see a sample closed, and how it looks from ground level looking up, and upper window height looking down.)

The sheer shades do close completely for privacy. The louver on the inside is opaque when closed and no one will be able to see in.

My tub is in front of the window, though looking out to the backyard. I have roman blinds (similar to those in the photo below), but at night, you can see the bather's silhouette from the outside. I'm sure no one is looking, but I always feel a bit uncomfortable.

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Plantation shutters would give you the complete privacy you want and all you have to do is adjust slats.

Aren't these wonderful but I don't know where they're from.

You could try adding a foundation light outside that points at the window. At night that would cancel out the silhouette that comes from the light being brighter inside when it's dark outside. Did that make sense?