Liners can be a consumable item; they're designed to last ~80-120 ski days. If your shells fit you well (and you have a decent footbed), a new aftermarket liner can work wonders. I was a boot fitter at a high-end PNW shop in the 90s-early 2000s, and still have some close friends in the industry.
Personally, I prefer Intuition liners. I've fit them for myself at home, but most people would be better off having a shop fit them for you.
Find out more (including a list of shops/dealers) here:
Intuition Boot Liners
Good luck!