What about a small curtain? You can get those a little larger than the actual window and you KNOW it's covered. If you can't find one, ask if someone can make one for you. Some of us here are seamstresses (to one degree or another... I can do basic stuff).
Another option is finding some contact paper type stuff that is semi-opaque... window film. There are some out now that have patterns in the plastic. It comes off fairly easily too... I don't know about where you live, but some place like Ace Hardware or Home Despot (Depot, really... but they have taken over) might have it as well. That way, you still get light in, but the privacy is assured (unless the window opens, and then you're SoL... unless you have a curtain).