Well because you aren't a very large person, I would suggest that you take up one of the martial arts that focuses more on using your opponents weight agents them, like jiu jitsu, tae kwon do, kung fu, etc. I would not suggest things like karate, or kick boxing. You may also look into learning ti chi, it doesn't seem like a martial art, however it builds muscil memory, if you were to add that to one of the other disiplines that could help a lot. Also I would suggest that you don't listen to the easter philosophy that they will teach, it opens you mind up to stuff that no one needs their mind opened up to.