To fit a new born and a 18 month old you need a One Size Fits Most (OSFM) Off the top of my head i can only think of pockets that are OSFM......

I like pockets, as you csn stuff more in for increased abosbancy.
BumGenious and Bluberry OSFM pockets are both good.
Although for newborn poo i would recommend either NB fitteds and a cover, or prefolds and a cover.

In my stash i have a bit of everything, i think my fave though is an AI2, ittibitti. Like an AIO, but the liner snaps off for quicker drying time. Sometimes i can't be bothered stuffing pockets, even though it only takes a second!!!

We used pockets overnight until DD was about 7 months, now she needs a more absorbent nappy, so we are using a pocket, or cover, stuffed with a mazalicious bamboo trifold. i have one dedicated night nappy, but they are quite $$$$. One other optiong that my friend used on her 2 year old is a BumG with 2 boosters in.

Am i making any sense today?!