Put on your new bra, then sit. Is it still comfortable? Sitting tends to give you a wider band size, and if you have a bit of a tummy, you will find this tummy moving up your torso once you sit down. If your bra is uncomfortable sitting, look for a bra style where there is an arched center panel- this gives the top of your tummy more room- or a bra style without an under-band.
Next, while sitting, lean forward. Does your bra gap in the cups? If yes, this bra style probably has too much cup coverage for you. A better choice would be a bra with smaller cup coverage.
Check out HerRoom.com for more bra tips and tests.