In reply to Joe Miller:
Hi Joe.
I bust up my lower leg about 12 years ago and gave up skiing as I simply couldn't fit my foot into a ski boot as I didn't have the range of flex to get it inside. I don't have a completely rigid ankle but very little movement and a partial weakness due to nerve damage.
I came back to skiing using plastic climbing boots but clearly they don't give any rear support and while they're good for the up they're bad for the down bits.
And then...
I tried a pair of Scarpa Maestrale. They have a front tongue which rotates completely out of the way and I can get my foot easily inside and then tighten up enough to ski ok downhill and even ok on piste for a day.
The Maestrale is one of several scarpa models with this feature on the tongue so its worth shopping around to see whats available. Braemar Mt Sports let me hire a pair for a day and then reduced the price of a new pair so I would unreservedly recommend them. Are you near there? Unfortunately Maestrales are insanely expensive.
There may be other boots with a similar sort of answer to your problem so its worth going to a specialist shop (when its quiet) and discussing your needs.
I do sympathise as skiing was a big part of my leisure time and I'd almost given up on it so it was a great relief to get back on the boards with a competent pair of boots again. Give it a try and don't give up.
pm me if you want more advice