I'm not qualified in any way to answer this question but here's what I've done in a similar situation:
jammed a cut to size piece of foam (I think it was part of a liner from a pair of old boots I picked up from a second hand store like like $5) on the top of my foot, well sort of the part that bends where your foot meets your shin. then you do your boots up and it's all tight and awesome
if all else fails, try that out before you go out and buy another pair of boots
peace:o