All diaphragm calls differ slightly in size as well and some may need to be trimmed to fit the shape of the roof of his mouth to get a good seal.
Literally any well known brand makes decent mouth calls that will generate solid yelps. As with anything, the more expensive generally means better constructed with better materials such as the latex.
Primos, HS, Flextone, MAD, Woodhaven, Mountain Hollow, etc are all good choices.
Just remember, the more reeds it has, the more air you have to move past them to get good sound. Most triple reed calls with wicked cuts on them are made for loud cutting and cackling.