Raw goat milk from the pet store. (No pasteurized one!) Primal has worked for us even when we had some GI imbalance (i.e. too much cucumber eaten or too much pool water swallowed).
New puppy (15 weeks now) gets Goats Milk Esbilac powder sprinkled over his kibble from day 1 and other than the first day when we brought him home he has not even had the usual cream cheese puppy poop. His is as firm as the adult one`s. No treats (as u mentioned too), other than organic baby carrots and antlers or himalaya chew.
Keeping the pup quiet at least an hour before and after eating is important. If they have running diarrhea skip a meal or two and just give the goat milk. Pick up right after pooping, especially if u had worm issues. And anyways, poop attracts all sorts of nasty stuff.
Filtered, good quality water only and be consistent, even changing water can cause upset stomach.
We wash food bowl after each feeding, meaning 3 times a day. We also get their crates wiped at least once a day and wash crate pads or whatever we use at least ever other day, using hypoallergenic wash pods and add vinegar.
Hope this all helps, with high energy sporting dogs tummy can be a challenge, it took us a while to figure it too with the first one too.