Alex - My dad went to have a pair of LL Bean boots repaired once after having them for years. They apologized and sent him a new pair at no cost. It might be worth it to speak with one of their reps to see if you can swap out your boots for another size.
As for insoles, I've used the one with the steel supports and even they seemed to shrink over time. On mine the toes actually curled up a bit, making the whole insole shorter. For that reason I think I'm familiar with what you're talking about regarding the soles sliding around. You might try cutting out a pair from wool felt. That would give you a bit of spring with each step as well as some insulation. Just a suggestion.
That's all for now. Take care and until next time...Be well.