Honestly, i would stick to the 00 or if you want grab a couple 000. You dont know how big bubs will be, and if its a bigger size you will get more use out of it. We were given 0000 singlets for Jesse (born 8lb 9oz) and they were only used for about 2 weeks. Because the singlet material is tight/stretchy, it wouldnt matter putting a 00/000 singlet on a 0000 baby. The length then will cover them and you just roll back any extra.