As an additional idea, discussed on other threads, you might want to consider a strap type of rig. I use a footstool, but I also like to play standing in some situations, or sitting with both feet on the floor, to avoid back problems. I originally used stick-on plastic hooks to experiment so I wouldn't put unnecessary holes in my guitars, but once I discovered that adjusting the strap as I was using the footstool gave me pretty much exactly the same angles for both hands and arms, I installed strap buttons on several of my instruments. So now I have 4 different postures: footstool, for "classical" concerts, strap sitting, strap standing (great for jazz work or leading a group while playing), and the Pace de Lucia right leg over left for flamenco or Bossa-nova sitting down, or even a short classical recital. This variety seems to be very healthy, as I experience no back, shoulder or arm pain at all, even when practicing several hours.
Lester Devoe Flamenco Negra
Lester Devoe Flamenco Blanca
Aparicio Flamenco Blanca with RMC pickup
Bartolex 7-string with RMC pickup
Giannini 7-string with Shadow pickup
Sal Pace 7-string archtop