I would recomend buying a platypus hoser. This is a basic hydration bladder only. They come in 1 Liter, 1.8 L, 2 L, and 3 Liter. They cost between 20 and 24 dollars and are extremely tough. They can be inserted into any pack you like.
I have one that has lasted 5 years of constant carry in the harshest of conditions you could imagine.
You might also consider buys a bite valve and drink tube insulator.
I am a firm believer of these types of hydration systems. It makes drinking easily accessible and relatively quiet. you can carry any pack you like and are not tied down to a particular brand. Platypus bladders are exceptionally tough and cost efficient.
Good luck and let us know how it all works out.