I think the company that does this is out of business, but I once got my boots at a store that had a machine that takes custom fit to another level: after trimming the forms to your feet, they put bags around your feet and all the air is removed to shrink wrap the mold to your foot. It looked weird and I got curious looks from other shoppers, but when they were done I had inserts that were at a high level of exactitude.

Or, if lacing your boots is an issue ... a built-in dial that tightens your boots.