Hearing aid holder to prevent loss.

I need a harness-like assembly that attaches my hearing aids to the back of my shirt so that the hearing aids don't get lost when they, inevitably, fall out.

The jury-rigged harness I put together, sort of, does the job, but the cord I use was not flexible enough, nor the right length. Has anyone assembled a harness that works well? What dimensions and materials did you use? Are there any ready-made, products available on the market? I have not found them.

Your suggestions are welcomed. .... wdc