Starches don't cause as much trouble as flours do! You have a few starches to choose from besides potato—cornstarch, tapioca, and arrowroot—and they are pretty much interchangeable when you are baking with them.
For Potato Starch, I really like Anthony's Organic Potato Starch. It's super light and I like that it's organic. At about $12 for a 2 lb. bag, it will last a long time.