I personally use 25-28mm x 6-8mm fletches, from the backside of turkey feathers. The really narrow part that gets always thrown away. The main idea is to use something stiff, but thin. From a common turkey/goose feather you can find spots where the feathers are thinner, so try those.
Later...try them all! Some prefer peacock feathers(?), those turkey backside's, vellum(rawhide), some razor blades....
With the fletching you can start from bigger fletching and then trim them down more and more, if the arrow still fly well.