Oh man, there are so many probiotic products on the market. Whole Foods carries a wide assortment of liquid and capsule type probiotics. Or a website like Swanson's carries cheaper
alternatives. Some of these already come with prebiotics, as does the linked example, which are the food for the 'good guys' so they settle better in your gut (fructooligosacharides as an ex.). Most probiotic products contain a Lactobaccillus type of beneficial bacteria, which consumes Lactose, so you're probably right to associate microflora with aiding digestion of milk.
If you want to learn more about this, "Missing Microbes" by Martin Blaser is a good general book about the microbiome and its relation to various modern day disorders.
Good luck with your experiment!