Would a white, half curtain work? Your house is probably too nice for this, but I rented a shack where I would paint the inside of the glass a thin white, leaving a portion nearer the top clear so that I could see the sky.
Any hardware store should have that window surfacing that you mentioned.
I painted the window on my garage back door (nobody can see it anyway).
How about that “frost” stuff in a can for Christmas? You might still be able to find some on sale - I wonder if that would frost the windows enough to prevent seeing through, but still let some sunlight in. Kind of like the frosted glass in my bathroom window?
Or - if you have the bucks - replace them with frosted glass.