Glasses leash with printed flex ends and a flex filament cord. The pictured set are in Ninjaflex but I have also printed them in other TPUs. Thread a suitable length of filament through them then use a soldering iron or flame to form a dimple on the end so that they are retained in the ends.

The design is for an arm with an end section 12mm x 3mm but it can be scaled in the slicer to fit other arm sizes.