I'm a little rusty on this.. it's been years since I've had a horse with navicular, but I'll try to help.
Back in the 80's (alright, I'm OLD) there was a surgical procedure that was relatively easy and inexpensive to help a navicular horse, it involved cutting the nerve on one side of the foot to deaden the pain. I don't know if it's still done, but it worked on a mare I had for about 3-4 years sucessfully.
There are also very skilled farriers that can shoe a navicular horse with padded shoes, which are very helpful. It's expensive, but will keep the horse pretty much pain free.
What stage navicular is the horse in?