Here's a solution for holding a classical guitar with a straight back and feet planted firmly on the floor that does not involve fancy new gizmos. It's a simple strap or sling made out of 30mm wide binding cloth from a sewing shop, but any soft belt or webbing would do.
I was struggling to play my classical guitar using a footstool, because this traditional solution put a twist in back and I've got a bit too creaky to stand this for long. The fancy little knee cushions and stick-on rests did not appeal...and looked rather expensive for what they were. Drilling holes in my guitar to mount studs for normal straps didn't seem right.
Then, after much searching, I stumbled across this strap idea at www.classicalguitardelcamp.com... which lead me to
• Mason Williams - Class... where you can see Mason Williams using it. By the way, Mason Williams used traditional solutions early in his career, but I guess he got creaky too and found the strap method more comfortable.
Anyway, I hope this video helps more people find this nice low-cost solution and experiment to see if it works for them.
I should add that I hold my guitar a bit high for even a classical guitarist, but it feels nice, so I stick with it. Others might like it a bit lower. Varying height and angle is easy with the strap. Whatever you do, if a playing position hurts, stop, take a rest, review what you're doing in the mirror, with a friend watching, or with a teacher, then try something new; do not just carry on doing whatever hurts otherwise it will just hurt more.
PPS If you experience any discomfort playing around with this strap method, then do not just continue