Hello Peterp1599
You do can purchase tickets on www.sbb.ch or on the SBB Mobile App without a swisspass-card. All you have to do is create a swisspass account at www.swisspass.ch.
The swisspass-card is just mandatory, if you also wish to purchase a Half-Fare travelcard, a GA or another monthly or annual travelcard. In this case, I recommend that you go directly to an sbb counter with a valid passport photo so that we can order your swisspass card.
For further questions please contact us: 0848 44 66 88 (CHF 0.08/Min).
Have a nice day. EllenvS.