If we could have found a 16 hand+ model for super tall hubby that met the criterea we would have bought it. We did look at some gaited horses in our price range but they aren't so common here and the ones we did see neither I nor the trainer were all too impressed with. With a 2 and 3 year old I couldn't be driving all over creation either.
About the knee issue though. All we did was slowly walk on level ground, it was both his and the new horse's first time out of the arena and pasture here so we took it pretty easy. When he did months of lessons he rode a well used old saddle at the trainers place. The new saddle we got for him and the new horse is pretty stiff and rigid and he felt that was the knee pain problem.