i tied a guitar shoulder strap, it seems to have worked!
a section of 1ft of braid, for the shoulder, with twisted cord for each end;
the twisted cord then works as a continuous set of notches for adjustment on the button / endpin.
small and lightweight, it stays on and fits in the guitar case 
it’s my acoustic guitar so it’s not very heavy;
i don’t know how it’d work on a heavy (electric) guitar.
i’ve used two lengths of 3mm poly cord of 8ft each
Matthew walker knots
and tassels so fresh i haven’t even combed them out yet
