Hi. Sounds like my DD has a similar shape to yours - the narrower crotch fits her better as well. When I get my next paycheck I'm going to buy Natty some more itti bittis!
My fave-fitting pocket for Natty is the bubba J pocket. Its also pretty cheap from memory, but you need to buy the boosters separately.
We just got some second-hand naps today from Natty's cousin. The ones that look like they have a narrower crotch on them (but we haven't tried them yet so don't know how well they fit or whether we like them!) are Beetlebums (AIO) and Bluegum Babies (fitted - needs a cover). Have google. I've no idea of where SIL bought them. The beetlebum looks like it'll be a good nappy...
Good luck! I'll be watching this thread