If you don't have a good boot-fitter near you, it might be worth the drive. Call, get an appointment made at good place and make a day out of it. There must be someone semi-close by that can (step 1) make you a good footbed, (step 2) alter your shell if need be. You really need to get a footbed first so you stop your arches from collapsing and consequently your ankle falling inwards. If you just get your shell worked on, your ankle will just move into that space and you'll still have a problem. (Step 3) sometimes getting some custom foam pads made to take up the space between the bottom of your calf and top of your ankle bone can work wonders too.
1. footbed
2. shell work
3. pads