Really shouldn't need anything if the quiver collapses in the center of your back. This is what holds the arrows closer and prevents rattling.
My Creger was too tight on the bottom, so I opened it up with a 9" long, 1/2" wide piece of soft foam. I don't push my arrows into the foam, just opened up the bottom more. Work your quiver with good conditioner, bend it, and wear it as much as you can so it will conform to your back.
Here is my heavy latigo leather John Schulz...note how the top and bottom remain "open" while the center collapsed to the contour of my back. No arrow rattle.