You should also be able to find discounted SBB fares with the app. One other suggestion, as the local trains get ticked into zones, which SBB doesn't always get right if you have a half-fare card, or a ZVV pass. So, make sure you have the right number of zones. There is also the ZVV app, but that's sadly only in German.

You will need a 3-zone ticket to get you downtown. The Albis Day Pass can be a good deal if you plan to head up the Uetliberg. But it doesn't include the trip from the airport.