You can try adding an elastic gore in to stretch them out a bit; I don't have any photos of an example, but essentially you'd cut a slit from the top of the boot down a couple inches (or possibly further- always best to not cut enough at first than too much and ruin it) and sew in a piece of elastic on the inside side to allow the boots to stretch out without losing their shape.
Help me get rid of my parasprite swarm!
Originally Posted by Moofingham
There is a vibe here that says "We're in this together! Through thick and thin fabric! Through cold water washes and burning hot irons! Though we might super glue ourselves to our projects, cut holes/gashes/oh-god-mom's-gonna-kill-me into the dining room table, we will stand strong together. Unless there is a 75% off sale at the Fabric store. Then you're on your own. And get the hell out of my way." <3