I use thick shoe leather. Thick harness or saddle leather works too. I've only used vegetable tanned leather for this. Cut it to shape, thoroughly wet it and remove the excess then use TB glue to glue it down. I use rubber bands to hold the leather in place until the glue dries. I've used leather and this method for a long time with good results.
Here are a few pic of how I do it...
here I added a second layer...
once the leather and glue have dried I saturate the leather with super glue. This allows me to shape it with a rasp and sand paper...
here is the handle ready for final sanding and the handle wrap of choice...
I also do the same with tip overlays. Same process.