I've been meaning to try some arch supports. I think part of what's always allowed my heels to come up/knees to cave so easily on squatting is my foot collapsing a bit inward. I think my heel will come up a touch regardless of whether it's weight shifting forward, or foot collapsing inward, as I think I have pretty flat feet. At least the supports may serve as a diagnostic of sorts. Any recommendations for some relatively inexpensive ones I can buy in a store or online (and don't have to have made)?