I purchased some 10 cm woven ribbon (3 meters) which came today. It's very much like a pink medieval design, so will look great with the classical guitar. Anyway I've measured it, turned in the ends twice for a nice seam and added a wide Velcro to each side. It means if/when I see a teacher I can adjust the height of the guitar just in case I get it wrong on my own.
For the ribbon I probably only needed 2 meters, but that would change for the neck to waist length for the individual person, I'm a 5Ft 3, so someone taller would need more ribbon. Oh for the guys webbing would work as well, and the clips can be brought pretty cheaply as well. A camera strap may work if it's long enough.