Small Camelbak.
It’s the least bouncy. You don’t HAVE to put a bladder in it. They come in numerous sizes and are comfy for running.
Order from REI, if you don’t like, send it back for full refund. They are cool like that.
This is what I did. I bought a small Osprey pack and take the hydration bladder out. It weighs next to nothing and has all the straps for a good fit.