The short quick answer to this is that any size larger than 256GB and has USB 3.0 should work just fine.  Make sure it is USB 3.0 compatible hard drive.  Minimum of a least a USB 3.0 connection, with at least 256 GB of storage. you can find 2TB storage for around $100 on various sites.

Checkout Microcenter and NewEgg for great deals on Hard drives for the Xbox One and Xbox One S

Xbox One S Hard drive