I am somewhat reluctant to answer your question as I feel that I am the only one answering you. There are many others who could answer.
Commercial yogurt, I feel, has been stripped of useful bacteria. Kefir, especially from reputable sources, seemed to be OK. I use the one from Trader Joes.
Depending on the product, the powder in the Bifidus capsules should be OK. I prefer a plain acidophilus powder, 1/8 of a teaspoon in one cup of warm water.