First thing - get rid of the footstool if you use one. ....
Seems to be a trend here.
There is nothing natural about having one leg in a weird position for hours. Even worse than flying long distance in a budget airline's "economy" class.
Consider a strap and play standing up. If you ignore classical players for a moment, the majority of the guitar players in the world play standing up at least some of the time. Putting a strap on is simply a matter of drilling two holes and putting in buttons to attach the strap. Or one button and tie the other end of the strap to the headstock. Alternatively a straps that clips into the sound hole. Check out AndreiKrylov's posts here in particular.
Certain simple stretching exercises can give some relief - I was shown two and a relaxation position by a physiotherapist decades ago and it helps immensely. I won't describe them as you need some one to show you.