Comment by lamp_book
I’ve seen people who seem to know what they’re talking about cast doubt that you could create your own probiotic yogurt in a typical kitchen since other strains are likely to dominate without a sterile environment and careful methods.
The strain you want has a huge headstart, and there shouldn't be much bacteria in boiled milk to begin with. Containers can be also sterilized with boiling water. Then keep it cool after it's done (14 hours). It doesn't seem likely that some other strain would dominate, but who knows.