Unfortunately television advertising often has just as much an effect on doctors as it does the regular person. Despite what they often say, most supermarket yogurt/buttermilk often loses all of its probiotic bacteria during the processing of it, to make it safe to eat. Along with that, a good majority of people are lactose intolerant and only some, but not all, lactose is broken down in the fermentation process. If you have any inflammatory symptoms, like ulcers, I wouldn't personally recommend dairy sources; but there are loads of great alternatives!
My personal supermarket favourites are sauerkraut, tempeh, kimchi, miso (I put miso paste in everything...), kombucha, and pickles. Basically any fermented food really.
I recommend trying to make some of your own if you find the time. I make dosa quite often on the weekends, which is a kind of delicious Indian pancake. Also tried my hand at making Natto, which is this strange but delicious sticky soybean thing. Had Salgam in turkey which was amazing too (it's a weird salty, spicy, fermented pickle juice).
Check out Wikipedia for a reasonably complete list: https://en.wikipedia.org/wiki/List_of_fermented_foods