My son was 7lbs 7oz at birth...we used kissaluvs sz 0's for at least two, maybe three months, and I just loved them. He was really long and lean though. I found with my bummis covers, the nb were too small, right from the beginning (at least for the kissaluvs - they worked with prefolds, but I tended to reach for the fitteds way more often.) But the sz smalls worked for us the whole time he used the kissalvus, so that's our plan this time around. When it was time to move to sz 1 kissaluvs, they no longer seemed to be able to keep up with his pee output, so we went to small fbs. I still have the fbs, though I am much more of a fitted/wool fiend now. I have amassed quite a few small wool covers, and a number of OS fitteds (SOS and Mutts, mainly), so I am going to see how those work for us once he's out of his sz 0 kissluvs!