I recently bought some adjustable rings for key chains, accidentally to be honest, I just didn’t check a size properly. Since, I don’t like leaving things unused I found them quite nice as a minimal rings. The greatest thing is that size can be greatly moderated.
You can check for something similar on Ebay: here, here or just enter for adjustable rings in craft section. It’s a bargain that can be turned into impressive necklaces or maybe you have idea of your own?