Not sure of your budget, but pure food is very good , it is a dehydrated food that you mix with warm water, I use it for one meal and use raw for the other one at the moment. you could also look at cold pressed food too, my dog does not do very well with extruded food he finds it too hard to digest and it comes out loose. He is also on the thin side but getting there now. It is a game of try and see , but these are the ones that have helped my dog raw and pure. Butter nut is very good too but a bit pricey. I hope that you can find a food for your puppy.