We measure your arch. We don't guess it.
There's an Aetrex Albert 3D scanner in our Matthews store. You stand on it in bare feet for about twenty seconds and it measures both feet separately, to within a millimeter: length, width, girth, instep height and arch height.
Aetrex sort their orthotics on two axes, arch height and whether you have forefoot pain. This is the medium arch with a metatarsal pad, built for movement. The scan settles the first axis. Where it hurts settles the second, and that's a conversation.
The scan is free and you're under no obligation to buy anything from it.