Swimtime,
It really sounds like the pool therapy is going to be key and thanks to your ability to put the pool in he has great access. My pool PT included a lot more than walking. I have a full sheet of pool PT exercises. Maybe a consult and a couple of sessions with a pool PT specialist might help. Sometimes the exercises can be found on line too. They can be very gentle.
Is the Lyrica helping? There are other meds to try if not.
I wish I could add suggestions on doctors, but Little Paw had some ideas.
For a recent car trip, I took two soft blankets and wrapped my leg in them, put them on a pillow and stretched it out over the console of our car from the back to the front seat to minimize vibrations. A foam pillow in the floor board helps on shorter trips.
You may already know all of this, but sometimes an idea will pop that you haven't tried. You have been very creative already in trying to help with his comfort level and recovery.
I wish you both the best. I hope you are finding some time to care for yourself too. ~mac