Kefir.net is probably a good place to start. Kefir has a way broader spectrum of probiotics than yogurt. It is extremely easy to make and the grains keep growing. A delicious drink IMO, kind of like buttermilk. when our daughter was little (she is 30 now), I’d make smoothies with kefir, a banana and any kind of frozen fruit. We just make it plain now and we drink it for the health benefits. for all those years (25 or so) that we had fresh goats milk we used that. Now we buy A2 milk, that doesn’t have the A1 protein that can cause so many problems. Those old Dannon commercials that shows the Caucasus mountain folk who lived so long, they did not eat yogurt, they drank kefir, that’s where the grains were discovered. There are grain sellers on ebay and etsy. Hope that is enough info, as I said kefir.net (a site that is pretty old) has more info.
Thanks very much for the information! We will look into it.