Mom, are the boot shells in good condition? Are you still pleased with how the shells perform for you? Consider just new liners.
First--shell-fit that boot. Remove the liner and put your stocking foot into the shell. Slide forward until your toes touch the end. How much room do you have behind your heel? Get something round, sharpie pen, penlight flashlight, etc., in 1/2", 5/8", and 3/4" diameters. Use those as a gauge. If you have 1/2" to 5/8" of space behind your heel, the shells fit you. If you have 3/4", they're probably OK. More than 3/4''--their future is as flower pots. If the length is OK, check the width. Pull the foot flaps open and look for about 2 - 3 mm of space on each side of your foot.
If the shells are OK, look into new liners. ZipFit and Intuition are the big names. I've had ZipFit, and they're tops. Friends have had both good and bad experiences with Intuition. Intuition sells way too many models, and shop clerks don't know what will work best for an individual and what won't. So--telephone Intuition and tell them about your boot shells and about your feet. 604-879-9231
https://intuitionliners.com/contact-us/
If they tell you what size and model liners will work for you, you can mail order from them and heat-fit them yourself at home. Or, when you know what model & size liners you need, a shop can order them for you and fit them to your shells.