One size fits all aren't a good idea if you want to use them from birth, they usually start fitting well at around 6 months.
Most of the nappies come with an insert, if you are wanting to use them overnight you may want to buy some more inserts to put in as well.
A fitted or pocket with a wool cover overtop seems the best way to not have leaks overnight. Makes for a large bum but the babies don't mind!
There is a topic under cloth nappies which explain the systems, I'd check that out to get an idea of where to start.
Otherwise, here are a few naps I'd check out for night use.
Ecobubs Wool Pocket\ - You don't need a cover over these. They come with an insert but you could add a folded cloth flat nappy to increase absorbancy.
Or something like a
Wam-Bamboo Fitted Nappy with a
Designer Bums Wool Cover - you just email her on designerbums@hotmail.com and she'll make one for ya. - If you want this nappy to be stay-dry you'll need to add a microfleece liner but these are easy to get hold of... ask anyone on the cloth nappy board and they'll sort it for ya.