Yes - footstool is standard, but it is a wrong standard ... it is like cosmetics of medieval times - like lipstick made from mercury..girls used that for beauty... it was standard...
Almost everybody (except youngest and strongest) have a back pain (according to answers in this theme ) but almost all continue to use it and to sit instead of standing/moving with guitar...Many people told me that they will sit because they would never put buttons for the strap on their expensive guitars...
Yes , we love our guitars! but...
I think it is in our eyes... it is been accepted that for the violinist or trumpet player it is normal to stand, but if guitarist will stand - then he will look... unclassical...folkish...amateurish... real classical guitarists are sitting, mot standing - it is how they should LOOK...
And we care about our look ... like women would use high heels (who cares that most of them will have problems with feet around age 50 years and older)
look is more important because it made us accepted...
I accept this. It is standard and normal for us... BUT,
Myself I care more about me feeling comfortable and been able to concentrate on music and not on the pain/discomfort in my back etc.
I would not sit if I could, but this my personal preference ... and my advice to you will be - why not to stand? why not to try?

I'd better speak by music...Please listen Andrei Krylov at CDbaby, iTunes, Spotify, Amazon etc. Thanks!