So far as I can tell the aggressively advertised Activa® is no different than any other yogurt, except for:

1. The claim of lower calories per serving, achieved by putting it in smaller containers so that the serving size is smaller.

2. Nearly double the price of anything comparable in my stores.

Foreign (import) yogurts may be subject to the same import rules that make it impossible to get "real" Camembert cheese here. The regs say that any imported dairy products must be fully pasturized before passing through a port of entry, so the live yeast/bacteria that "finish" a Camembert must be killed, and what one can purchase - in most outlets - won't "ripen" appropriately.

Greek yogurt (imported), although sold here along side the "white cheddar posing as Camembert" may be in the same condition, although I can't confirm that it's also required to be "fully dead;" and a domestically produced "Greek style yogurt" might be permitted to contain living organisms.

In some grocery stores here, occasionally and sporadically, one may find skim milk with added lactobacillus. I've used it for several decades when it "just felt right" to pick up a jug, and intentionally after any antibiotic treatment. It seems to be a help, although I haven't attempted to collect clinical data.

Lactobacillus acidophilus capsules or powders can be purchased at "health food" outlets, and could be used if a need for supplementing what's in your gut is perceived, although the strength and viability of what you get - and the price you may pay - may vary by quite a lot depending on the mood of the seller(s).

Bobad's suggested alternate source is certainly worth considering (by some), although it should be noted that being the primary bacterial flora doesn't mean it's the only flora, or even that it's always present in all the places where it might be expected.

John