I had no great desire to add the zipper to the dress until the perfect zipper, a silver-coloured metal two-way separating zip presented itself to me in a tiny semi-basement Toronto store stuffed with fascinating notions. I blogged about my flying trip to the Leather and Sewing Supply Depot here.
Now the zipper wasn't the right length - it was too long by about a foot. But when you're dealing with zippers, too long is not really a problem. If you have pliers and aren't too intimidated, it's pretty easy to remove teeth and replace the zipper stops where you need them. There are how-to videos on You-Tube and other sites.
Replacing the slider if you accidentally pull it up above where you removed the teeth (oops) is a little bit harder but also not a show-stopper. I had to do this - not, I hasten to say, because I pulled the slider off accidentally, but because the zipper I bought had the top slider on the inside of the zipper so I had to take it off and replace it on the other side. I would explain how I did it, but I'm afraid it would be pretty incomprehensible. My advice, if you ever need to do this, is to search for a video on line.
As to wearability, apart from the first little frisson of cold when I put the dress on, the zipper is completely comfortable to wear - it's not even noticeable.