There is a number of different armrests available. Most of them are using adhesive strips for fixing to the body which I personally refuse due to the risk
of chemical reactions between the glue and the guitar surface. Others have suction cups and may work well on closed polishes but not on open-pored surfaces.
The "Guitar Armrest" uses a padded clamp with two metal screws and can be attached very simple but precise to the guitar body. The shape fits very well to small and medium sized bodies and there is no risk to damage the varnishing. Length and contour of the armrest are designed perfectly to meet different
playing positions without becoming uncomfortable or looking too dominant.
I fully recommend the "Guitar Armrest" and would appreciate very much a modified design for guitars with a thickness of less than 8 or more than 11 cm.