For my first, I bought some 0000's and some 000's. He never fit any 0000's, being 9lb4oz. My second was smaller, 7lb9oz and fit 0000's for a few weeks.

My advice is this - to buy mostly 000's because even if bub is reeeally small when born, they will eventually reach 000. Buy enough 0000's for a couple of days, with #2, I had about 3 days worth of 0000's, and then I sent my mum and dh shopping for more. If you send your dh shopping, send specific written directions on what to buy, or send him with a sample - depending on his level of vagueness.