a good mixture of wrestling, boxing, muay thai and brazillian Jiu-jitsu is my suggestion but that can take time.
For a short trip to combat effectivenesss i recommend 3 elements to concentrate upon.
1. Punching, punch hard and fast, shadow box alot, hit the bag with and without gloves. Spar with someone with gloves on so you can handled pressure. Boxing by far the most effective form of striking i have seen for the hands. Start by learning to put your shoulders into your punches, learn the proper mechanics of a jab, cross, hook & uppercut.
PUNCH HARD, punching lightly or weakly does noone any good.
2. Defense, develop your defense. You can't do anything if you get knocked silly and being small (i am 150 lbs) you are liable to getting knocked out easier than other folks of the larger persuasion. Boxing defensive concepts are good up to a point but remember much of it is assuming you have gloves on. Spend time with someone trying to take your head off as you try to not get hit using your elbows. forearms , hands and footwork. slipping punches is the best way to deflect power but takes finer timing and control. learn to move your head after you punch and as soon as your opponent punche, develop the habit of raising your hands in front of your face for protection after every flurry of punches you pull off.
3. get comfortable in the clinch, you will be there regardless of desire, lok up some Muay thai clinching info online, its a great tatic to learn to start clinch tight and start laying in the knee strikes as fast and hard as you can do them, it takes great skill in clinch work to avoid sdome big shots once you are clinched and the knees start flying.
From clinch its just a slip to the ground, learn some ground work, you will end up there no matter what you want.
and as an addition to all this i recommend stick work, get a flashlight or a extendable baton ot just a stick. Swing it alot, again speed and power are essential as well as accuracy.
an excellent comparitive martial arts resource is
Stick Grapplers page