I'd work with a production model where you can try on basic pieces (pants, shirt, jacket) in the store, then browse online across multiple styles that work for that size block.
So you try on the store's pair of grey pants, 16, regular length, and find they fit. Then you go on the website and can choose from multiple colors/styles in that size, and you'd know they'd fit. Made to order--which in the current garment manufacturing world wouldn't be terribly hard to accomplish.
Also, pockets. And I'd manufacture somewhere that young women didn't regularly die in fires.
