I Love the WNNL but I bought a large as DD is on the cusp of M & L and it's pretty high in the rise, so have bought a couple of pre-loved mediums. I'm really liking goodmamas on her and still so many to try! yay!
Tots Bots stretch are nice and slim, but I think the new Itti Biitt Boo are slimmer - more like the fit between the legs of the old-style cotton Tots, and being popper fastening rather than Aplix are not too bulky at the waist either
We've just invested in some Weehuggers, which are amazingly slim and well fitting, and look so adorable! The outer wrap part of the nappy can be worn multiple times, all you need to change is the insert. Any inserts can be used, although they do come with their own, we use them with Flip Stay Dry inserts.
Day to day we also use Tots Bots Stretch, which are fairly slim if you use them with just the regular insert, but if you need to boost them they can become quite bulky, and they also take forever to dry!