I boost the flavor by blending other cheeses with my mozzarella. Try some cheeses which are a little fattier than mozzarella. Among I ones I often might use are cheddar, asiago, fontina, provolone, kasseri and caciocavallo. Use sharper cheeses very sparingly, the flavor can be too sharp if you use too much. Also, since these cheeses are richer than mozzarella, you will get some oiling off from them.