A blazer in a dark neutral is ideal to have as a dressy-causal jacket. They are great over any outfit, and if you have a particularly more fancy one, it can go over an evening dress too.
Pick a color that looks good on you. Pick buttons that are in line with your body proportions.
If you're larger chested get a 3 or more button tailored suit; it will give enough support for your chest. Also, make sure the there aren't any design lines on the upper arms that touch the breast area.
For a small chest gal a low one button, with detail on the collar would be great.
For a gal with a belly, make sure it's skim fitting in the belly, no buttons on belly, and make sure it's long enough, not hitting at belly area, resting on hips is better.
An hourglass body would look great with some tucked-in waist details on the blazer.
Try on several styles within these guidelines and get the best style in your best dark neutral color. You'll find it working with many of your outfits.