I've used store-bought dairy yogurt (I'm not THAT allergic to milk), store-bought cultures (usually dairy grown), probiotic pills (non-dairy; split them open and guess at the dosage ).

Where did I just read that big-brand store-bought dairy yogurt has the most stable and vigorous cultures, and the sugar and additives aren't enough to hurt your initial batch? Was it someplace someone on this thread had linked to?

I don't make yogurt often enough to keep a culture going. Now that I've discovered hemp milk yogurt though, I just might!