Hey Fitzy...here's another maternity idea I stole for my bloat. My friend who was a CPA owned many expensive suits and could not get a whole new wardrobe for her pregnacy. This works for skirts and pants as long as you wear a shirt that hangs over them.
Use a rubber band through the button hole and put both ends of the band around the button. It gives me stretch in the pants and I can change the rubber band to a different length if needed. Most zippers will stay partially zipped in place, but I use a safety pin if it does not.