The first time we visited Bali in 2014, we didn’t even know about Bali belly and we didn’t have any problem. We were in Malaysia first, though, and in Malaysia a vomited my soul (and emptied my guts in liquid format) after getting a dodgy drink in the street (I will never buy a drink from the street again).
Anyway, long story short, many forum posts suggest to drink Yakult in Bali and already 1 month before your trip to Bali.
In Switzerland you can buy Yakult at Coop, check Probiotic drinks (including Yakult) at Coop.
You can find also Probiotic at Migros.