Robin, I'm not sure I do know how to make initial picks better than you (I liked yours, here!) but for what it is worth and in case it helps you or anybody, I do have some tricks up my sleeve, as a result of my long practice. (For years I lived in a place where in person shops were limited pretty much to the Gap.)
Here is how I did it. I made city trips once or twice a year and tried on items at various stores -- not to buy, but to figure out the sizing. Of course I concentrated on brands I liked (in theory) and that I'd read about here as fitting well on near-petites with my body type modifiers. (In other words, I read Angie's reviews assiduously.)
Once I'd narrowed down a few makers that had a good chance of working, I focused most online shopping on those and/or on those I can get. (In Canada, so my options are much more limited than yours and apart from a few, returns cost me money -- a lot of money. So I need to be extra careful).
Truthfully, for me, that meant BR, J. Crew (not so much nowadays, but that's another story), and sometimes for tops/jackets, Zara. Eventually, I branched out to Everlane and Boden (with mixed success) and a few others.
I also looked at the Finds a lot and if I found something I liked, I checked to see if the person collecting it had body type modifiers similar to my own. Then I would check to see if I could get in Canada (not always possible.)
I let a lot of potential orders go because I couldn't be confident of the brand's fit. I made a decision in some cases (e.g. Boden) that it was worth ordering and paying for some returns just to figure out the brand's sizing. (We have no Boden stores in Canada.) And if I wanted an item from Nordstrom, I would ask on the forum how it fit before hitting buy.