DD1 who was just under 6lbs (2.7) wore 00000 for about 3 weeks and then lived in 0000 until she was about 4 months old but she is teeny even now...

DD2 was 7lbs5oz (3.43kg) and was in 0000 for almost 2 months and now (at 3 months) is transitioning into 000.

I would recommend packing some 0000 singlets, but if you are going to go for a bonds wondersuit, go for a 000...those things are sooo tiny lol!