Been there, done that. A built up leather handle works well and will stay in place.
I started out making non-bending handles, e.g. the "long-ass handle bow" that had a handle section 14" long in a 68" bow.......stupid beginner mistake. Now, i'm more likely to let the handles bend and use the whole bow. My last several bows have been truly "minimal" bows: 60" overall length, 25" pull and about 50# with no handle section at all!
I have just been winding seine-twine around the handle portion with a floppy rest on the left side. These bows have been coming in at 314 and 435 Grams total with grip and string, and are a pleasure to shoot.
My suggestion is to build up a leather handle and cover it with a grip......and make lots more bows.
piper