When I bought my boots online I just did research on boots that had the flex I wanted. Then I ordered 3 sizes from Salty Peaks and returned the ones that didn't fit. Most places you only pay like $5-10 for a return label. It's worth it for the convenience imo.
Besides my local shops had hardly any stock in by January, so I would have been stuck with some ugly ass single boas that didn't fit quite right.