Yeah. It's a remarkable problem. There is a clear solution that is happily used for men. You tell people what to measure then have the clothes sized for the various dimensions.

Charles Tyrwhitt have this guide where they tell you what to measure for shirts :

https://www.charlestyrwhitt.com/au/size-guides/szg-formal-sh...

and for trousers :

https://www.charlestyrwhitt.com/au/szg-trousers-4-2021.html

Presumably some online shops for women have something similar?