Replying to Worn down boot--> wobble problem.

my boots are worn down in toe and heel creating a gap for my boot to wobble, both in the front and back, I have toe height adjustment so I made the toe better, but what can I do in the heel. I can't get replacement heels because the screws are stripped. I don't want to buy new boots because I have new boots already but they are too big.(not returnable)

I've seen Delorme put cardboard under his heels, any other ideas?
Thanks.