This might sound crazy, but I was thinking the same thing as your wife

But I also thought of a possible solution - you know those curtains on roll you can get from Homebase (or B&Q) and cut them to size? I was thinking these could be fitted in a way that the sides of the curtain would be imbeded into those plastic courtain rails fitted on the sides of the curtain (sort of like the expensive Velux curtain do). It would look neat and always stay in place and seal the window completely. Only thing I didn't work out is how to keep them in the place at the bottom of the curtain itself...
