I personally am wearing two-button jackets, because they were more flattering than the one- or three-button styles.
I don't think the number of buttons is nearly as important as the following:
1) The correct size of both jacket and pants. Try suits on while SITTING DOWN to see if they'll be comfortable (i.e., allow you to breathe and speak normally). This is not the time to be vain, or buy something promising yourself you will lose weight. If you are uncomfortable, you will not only be miserable, but may not perform as well as you would have otherwise.
2) An appropriate top under your jacket. Anticipate possible bending over, raising of your arms with your jacket unbuttoned. This shouldn't create an issue with showing inappropriate skin.
