I bought the natural bottles classic is discontinued alr) all in the clear series. It works well for my daughter since Day 1, no leakage or teats issue. I would think 6 bottles is good to start with since the sterilizer can only fit 6 at a time. Amazon offers it at a lower price, I actually bought difference sizes and the different teats all at once. I bought about 10 bottles and that's because I like to prepare more than needed. It's good to buy the newborn starter kit which comes with 2 newborn bottles and a few other accessories to try out first and see whether your LO likes it.
I brought 1 Avent natural glass bottle, 2 Avent Classic and 2 Avent natural bottles (All in white). I wasnt sure which bottle suits him. I found this blog quite interesting. The mother gave her views on differences of Avent Classic and Avent Natural bottles. http://thelovingmum.sg/2013/04/feeding-bottle-woes-over-with-new-philips-avent-natural-bottles/ Subsequently, my baby does not like Avents bottle and it leaks from drinking. Hence we changed to pigeon bottles.
I bought 4 comotomos and 2 mam bottles to begin
Maria