Bio-K is one of just a few probiotics that has been proved to work. I don't mean to sound like an advertisement, but there have been double blind studies done. I don't have time to look for the results, unfortunately. She also felt that a high quality organic yoghurt was a great way to maintain healthy levels.
Bio-K is a fermented milk product and is, I gather, loaded with probiotics. I used to take it daily. Usually in the morning.
It's not cheap, but not stupidly expensive and you don't have to eat an entire container (as the makers of Bio-K suggest). My naturopath had me on two tablespooons a day, which made one container last three days. She felt that it was such a high quality that it was worth me taking even with a suspected casein sensitivity.
So there you are. My two cents worth.

Love and Warm Hugs,