I don't buy as much Q fashion as I used to, but I've always used the garment measurements for items I'm thinking about buying. I look at the chest measurement if I'm buying a top or jacket and the low hip measurement if I'm buying pants. Works most of the time. It's one of the things that IMO makes Q clothing shopping better than online retailers who only post body measurements. I also check reviews, the fabric, and whether the garment is manufactured to be a close fit or loose fit.
I still prefer to shop in person and try things on for the best results, but brick and mortar places aren't offering as many sizes, styles, & colors in store as they used too, so I do my best when shopping online.