The only problem with one-size nappies is that you can be kind of overwhelmed with poppers at first! I know the MotherEase one-size scared the crap out of DH, and he was used to real nappies. Get a couple of different ones to try out - you can get them second-hand from the Nappy Lady's Classified Ads.
The different kinds are:
pre-folds (where you fold up a padded cloth and push it into a waterproof wrap, and put on the wrap - not idiot-proof but very cheap),
shaped or fitted (like Tots Bots - often velcro, can be poppers, ever so easy. NOT one-size, although my DS is wearing the same size at 18 mo that he wore at 6 mo. You need to put a waterproof wrap over them),
one-size (generally shaped but with a plethora of poppers, wrap required),
all in ones (dead easy, usually poppered, no wrap required, quite expensive, can come in one-size),
pocket nappies (these are shaped nappies but the top of the back isn't sewn up, so that you can stuff it with inserts - eg microfibre cloths, proprietary boosters, prefolds). Some pocket nappies are 'all in one' so no wrap is required.
Wraps are waterproof outers, they can be poppered or velcroed (poppers last longer). Generally they aren't one-size, but each size lasts for yonks because they're often loose-fitting. MotherEase are generally accepted to the be the best.