What about pocket nappies. the wonderoo is a birth to potty nappy. The advantage here would be that you could use every nappy for every size child.
Or if you want to go one size birth to potty then you could go for the motherease you'd need wraps with these.
Another oprion in the pocket nappy is the minki no need for a wrap and they are gorgeous.
the swaddlebee is new to the uk but works on the same principle as a wonderoo. The main problem here is that its sized so you'd need different sized nappies}