More horsepower from a crf 230?

i have geared it down by getting a drive sprocket one smaller than stock in front.... the other day i put the original sprocket on and was flying around 10 mph faster than usual. i love the speed but it doesnt have as much power...... also i am about 220lbs so i need a better shock spring so i can jump. i can not do a big-bore kit but maybe an exhaust and a few things that arent to major. what parts would you recomend i get for my bike and where should i get them from??