I have 9 week old twins who were 5lb 14 and 5lb 11 at birth. I had a mixture of different nappies that I tried with them. The Lil joeys were oh so cute but leaked like anything after the first week. The xs BG aios were very trim but would not last more than a couple if hours at best without being saturated. I found Teenyfits also leaked even with a little lambs bamboo booster
My favourites were Diddy diapers, bimbles and xs sandies (but only if they were boosted with a little lamb bamboo booster) paired with a thirsties wrap. I also liked thirsties fab Fitteds but these also had to be boosted with a preemie prefolds or little lamb bamboo booster.
At 9 weeks my twins have only just hit the 8lb mark so we have plenty of growing room before they are out of my newborn stash and Into the smalls or OS nappies.