Hopefully a pro groomer or breeder here will post too, but here's my two cents
Go to
www.dogfoodanalysis.com/ for a list of premium dog foods. If you're trying to work on the hair coat, look for one that is a little higher in omega 3 and fish oils, maybe even go with a food that has salmon as the main protien source, just make sure it's an "all life stages" food since you have a puppy. Most high quality dogs foods will have enough for the average dog in it though.
can you post a close up pic of your puppy? I doubt the hair is "too" thin unless something is going on like allergies or a deficency in something, but you most likely would have picked up on it yourself. My Alice has a coat more on the "thin" side and yes, the hair on top of her head is more thin and hard to keep a top knot in at this point.