Onesize Baba+Boo (BTP/Size 2) will usually fit from around 8-10lb and will continue to fit through to potty training.
If you want to use cloth nappies from birth, you may prefer the Baba+Boo Newborn range (which often fit from about 6lb).
OneSize nappies include a waterproof outer with a fleece lined inner which creates the pocket for the inserts, each Baba nappy includes two super absorbent Bamboo mix inserts.
When your baby is teeny tiny, you will normally only need to use one insert, which should last up to about four hours during the day. Once your baby starts to grow (which is always too quickly!) you may find the nappy doesn't last quite as long, it's then the time to add the other insert for extra absorbency.