I'd recommend lookig at the P'tits Dessous mini-maxi. It has the best size adjustability of any birth to potty nappy I have seen, really fitting form a pretty small newborn through to a very chunky toddler, without builders bum! It's a pocket, quite similar to Fuzzibunz, but with a much better adjustability. Popper fastenings at both legs and waist.
OK, it doesn't ave the same funkiness of WNs, but it's god quality PUL, will wash at a good temperature (unlike some which state no more than 30º!) and for a BTP m=nappy, I think it gives the biggest range of sizes.