Most insoles are made of thin foam that can easily be trimmed with scissors, unless they have gel inside or something. You can layer them too if one pair isn't thick enough. For that, I buy the cheapest ones I can find. Unfortunately you couldn't layer cheap ugly insoles in open sandals or heels. For sandals or heels, "Dr. Scholls For Her" fit quite small and are very comfy, and I'm pretty sure you can trim them, but once you stick them onto a pair of shoes they are hard to get off again.
Hope that helps!
