Yet another 'cusp petite' chiming in (I'm around 5ft3 on on a good day - & am definitely no 'waif', lol)! For reference, my shoulder to natural waist is 16" but to just above my hips is 20" - so I can *sometimes* wear regular bottoms, but am otherwise short waisted (sleeves are often too long).
I'm unfortunately going to have to echo others here on the importance of shopping online if you have any sort of fit 'issues' (which, let's be real, is most of us). Even for me, I use the petites section back home (in the UK) but ironically my limbs are now too long for the 'Asian' sizes out here (in HK)!
All is not lost though - if you like thrifting/ brick & mortar shopping, then I'd recommend buying your fun accessories & completer pieces there (like toppers) but stick to your basic clothing online.
PS: I'd recommend Seasalt Cornwall (no surprise there, lol) - they have a petites section, list garment measurements, often use natural fibres, & do free shipping worldwide (above a certain amount). I also like that their styles are usually fairly classic, but with small updates & fun prints.