I wore out the pull on my year-round yellow cycling jacket and needed to replace it with something large enough to grab with my gloves on. I started simple and then made a few improvements a month or two later.
First generation tag in use.
Although I could operate the zipper ok, I felt that tugging was working against the direction the zipper wanted to move. A longer and more flexible pull would work better.
A wider pull would have a better feel in the hand but wasn't going to be such an easy one-piece replacement.
//scad.fed.wiki/assets/viewstl/viewstl.html?stl=http://scad.fed.wiki/assets/zipper-pull/flex-zipper-pull.stl HEIGHT 370
I also increased the joint radius. With only an outside radius my first design was difficult to install. My new design included inside radius which might have been a little too large because the pull seems loose. If I loose the pull in use I'll measure the attachment point and match that for my third version.
Flexing has been concentrated in one spot leading to failure. Distributing the flexibility will resist this but might not prevent it in a material not designed to be flexed.
Simple solution is to control how deep the slots go into the pull. Maybe linear? Logarithmic?