We had a certain amount of success with Kushies (also Boots own brand all-in-one nappies, which are similar). They have the waterproof wrap built in and fasten just like disposables (with velcro); the only assembly required is to put a sheet of lining paper on. However, they do depend on the child being about the right size for a good fit.

Even when we were on washable nappies "full time" we still used disposables overnight and when out of the house for any length of time. They were definitely more convenient and lasted longer between changes. And we went back to disposables when he grew out of the Kushies, so overall we haven't been a great advert for the (supposedly) ecological method. (None of this "wash at 30 degrees" either — they were washed at 60 on the full programme.)