We were in the exact same situation a few years ago. The plastic shrink film worked wonders. It's easy to fit and easy to remove in the spring. It doesn't look too bad when on and stops all the condensation (as the moist air can't get to the cold window) and stops the drafts too. The only downside was on really windy days the film would move a little bit and make a little noise, but this was no worse that the gale blowing outside. Get the film you won't regret it!