I personally would get two small puppy kongs, and two medium puppy kongs.They are not expensive, and when they are no longer needed I pass them on to friends with puppies(after a hot wash in dish washer!)
The rubber in the puppy kong is more flexible and chewable.
A favourite with Carrera, especially during this hot weather phase is
Blend two slices of wholemeal bread, one small carton of unsweetened probiatic plain yoghurt, and one small can of tuna with olive oil(olive oil drained).
Plug small hole of Kong with a little of the wholemeal bread, pour blended mix into Kong and wrap in foil and freeze for 24 hours.
Another favourite is ripe banana instead of the tuna.
Remove Kong from freezer 15 minutes prior to feeding......and I guarantee u a happy pup. Also fantastic as a diversion when introducing a diversion for separation