I got quite a few vests and sleep suits as explosive nappies and spat up milk feature a lot these days and I can change him 2-3 times a day. More the milk than the nappies though for us. A few of us have found Asda sleep suits are a bit smaller than others length wise so I'd also get some 0-3 ones too, just in case you have a long baby. Saying that, Cole weighed 7.12 and I had to go buy a few early baby bits because some newborn stuff swamped him. I think I had about 12 vests and sleep suits in newborn and half a dozen of each in 0-3 but plenty of people bought us 0-3 sleep suits so we've got loads now
I've found that Asda are quite short in the body and Primark newborn stuff seemed tiny. My favourite sleep suits are his Matalan, Tesco and Boots ones.