Well, here's the problem... You want thicker leaves, but in order for you to receive thicker leaves you must first gain thicker branches. To get that, you will have to cut back you branches, not too far, but leave only a few leaves on each small branch. I did this on my Serissa, and this will cause new foilage to grow in a smaller area, which equals overall more foilage, giving you a nicer look.
