After being in the water for a while, getting out of the pool to the full pull of earth’s gravity is tiring.
Have a ledge in the water, that when you sit on, inflates and pushes you up above water level so you can quickly step onto the perimeter of the pool.
It’s more than likely that whatever chair you choose you’re making some kind of compromise. It was not designed specifically for you.
Build a sensing and inflating mechanisms into the chair. The sensors will sense when some of your muscles are beginning to lax and would cause the right element to inflate in order to compensate for that.