First of all, thanks for the replies!
I live in Vancouver and I'm not sure if shops still carry their molding equipment or have experienced staff around during the summer time?
I agree, I think the Lashed that I bought are probably 0.5 size too big, considering the heel lift. Getting J-bars seems like a quick & dirty way to fix the situation but I should really find a pair of boots without any of those issues in the first place. Especially since the boots are still new and I got them at a pretty good discount (can't return them because I bought online in the States).