Thanks girls - I used both and she went 6 hours during the night with it fine and it probably could have gone a bit longer.
I haven't tried the sized ones but I love the one size! It's a great fit once you've spent some time fiddling about with the adjusters. I'm staying away from sized nappies (unless second hand) as I don't want to waste money on something she'll outgrow!
Will look out for the mommys touch inserts, thanks! Have just bought some wonderfull inserts from classifieds, and a blueberry one size insert to try out too