Moms that had their baby/babies!

So I'm a first time mom and making my registry for my baby shower. I had multiple people tell me not to get too much newborn because they grow out of them quick. Well I want to put sizes up to 6-9 but don't know how much of what I should get. How many onesies, pajamas, baby pants or whatever should I get for each size all the way till 6-9?