I liked the design of the original 22mm watch strap this is based on, so I took the model and made a few quick changes in 3D builder:

Reduced width to 18.6mm for a snug fit in a 19mm watch band size
Reduced thickness in the centre of both parts from 4mm to 2mm, making it more flexible and comfortable
Remodelled the loop for the strap so it fits the new parts

Printed this in TPU for flexibility, then dremel / hand sanded down the top face to give a nice matt finish. Also drilled out some of the stringing parts in the holes and hot air gunned to finish.

Note the photos are of the original version before I remixed it to make it thinner to fit better.