Hey, Griff, welcome to the fire. I can almost commiserate, I'm missing a toe from my left foot and wearing a "half shoe" thing on my right foot so a wound on the bottom can heal up. At least I don't need crutches... yet
Boots aren't the only option, there are also Army shoes, bootees, brogans, whatever you want to call them. They're ankle tall and lace up. Lots of them were made and worn out before, during and after the War of the Rebellion. It should, I think, be pretty easy to get one of them on your prosthesis. I recommend getting in touch with these people and giving them a chance to help you out:
Fugawee Corp.Mattimore HarnessRobert Land FootwearWhoops, I just noticed River City John has already given you a link for Mattimore Harness and Robert Land. Let me just say, they make
really nice boots and shoes. And RCJ, thanks for the link to Stacey Adams Shoes, they look really good.