If you are concerned about weight gain, do some moderate form of regular exercise. If you have not been exercising regularly, consult your physician for a practical exercise program which is safe for you. Smoking will just complicate the original situation while creating another crisis, a relapse into the nicotine addiction. Don't debate with yourself how much you want a cigarette. Ask yourself how do you feel about going back to your old level of consumption.
Smoking is an all or nothing proposition.
Save the money you usually spend on cigarettes and buy yourself something you really want after a week or a month. Practice deep breathing exercises when you have a craving. Go places where you normally can't smoke, such as movies, libraries and no smoking sections of restaurants. Tell people around you that you have quit smoking. Remember that there are only two good reasons to take a puff once you quit.