"I'm petite and slim with a large chest, and it's difficult to find blazers that will button and also look proportional elsewhere. If I leave my blazer unbuttoned, it looks silly because my chest makes the blazer drape far away from my body. Is there anything you can recommend to fix this problem?"
I have thought long and hard about your conundrum and have even consulted colleagues. Here's what we all suggest: Ditch the blazer. Opt instead for knits ̬ a cardigan or a shawl/wrap. The benefit to the knit is twofold: It will drape to mimic your shape, and it can be belted. Even a shawl/wrap can be belted. To be blunt, a tailored woven jacket will be a perpetual problem. Actually, any woven will present a problem because it won't be malleable or shapable. Trust that a cardigan or wrap will provide the same semblance of sophistication and polish that a blazer does, provided that its silhouette is simple and refined (no epaulets on the cardigan, no fringe on the shawl) and that it is a dark or deeply saturated color.