I would recommend something like kickboxing or muay thai boxing. It will probably be more of a workout and less complicated than kung fu. Many places do a type of MMA that will probably be advertised as kungfu and kickboxing which could be good too. Research a few places and go to a few different classes, you usually get the first one for free or at least can sit in and watch. The only problem would be if you need to group up during the lesson but when I did martial arts the instructor always put me into a group rather than watch me struggle.
Other than that jogging in the early hours when no one's about and a few weights/situps at home a few times a week but I find martial arts much more interesting and rewarding.