I usually buy nonfat plain yogart. Vanilla flavor is ok to give them. Just not anything that has fruit in it. Eleanor loved the vanilla. I only give them 1/4 tsp at a time, 1x a day so I dont worry about too much sugar because it's so slight in that small of amount.
I've looked for that BeneBac and never found it at PetSmart. Finally asked a clerk last time we were there and it's not stocked at our PetSmart.