My in-laws all love their reading glasses with a split-bridge joined by magnets, and a built-in loop around the back. I think it’s these: https://cliceyewear.com/
If you don’t mind the aesthetics (though I personally can’t get past them), they solve the same problem as your string in an integrated way. Plus they rest more like a necklace, since it doesn’t require as long of a loop.
That's interesting. I won't be trying them though, I hate frames, it is bad enough with frameless but frames really spoil it for me. One brand in particular that I've found makes glasses that are almost invisible to me when I'm wearing them and that's the one that I've stuck with for the last couple of years. If the tech described here comes to general availability I'll be super happy.
If you don’t mind the aesthetics (though I personally can’t get past them), they solve the same problem as your string in an integrated way. Plus they rest more like a necklace, since it doesn’t require as long of a loop.