The boat pouch is a really good design for beginners.  It was started here on the forum, a member came up with it, the CAP PAUL as well.

I use moose hide, its super soft, and supple. Its an amazing material. I use anywhere from 4mm to 8mm thickness

Welcome to our world 🤓

Can't argue with Joe's suggestion , couple of points; don't get too hung up on which and what. Make 2, 3 or more from the same piece of leather. An old jacket, a piece of furniture leather or scraps off the interweb, loads on eBay and gumtree. Then play. Use paracord, use string, try braided string. Oil the leather, mould it, cut slits in it or shapes out of it.
Above all enjoy experimenting and find what gives the results you enjoy using.
Funnily enough after all that I still like my paracord and seatbelt sling the best.
Other point is a looped knot for attachment spreads the load better.
Cheers,
Zud👍

My favorite has always been the Apache sling. You can modify it however you choose. Paracord is also very good for a cord material.