weight lifting won't stunt your growth, its unproven. There is a tendency thought to lift too heavy at a young age.

Keep the reps very high. Bolx to flat benching its for cheats and wankers who can't lift and don't even bother benching on a smith machine!!!! Use upright cable crossovers if you can and vary the andle, cable flyes lying on a swiss ball. If you do have to use a bench try incline flyes to isolate the chest then chest pressing with dumbells never a bar!!!

Having said that the king of all chest eercises for Boxing and MMA is press-ups. Try doing them slowly with corresct technique and watch your chest, triceps and dlets tone up!!! I know lots of people who clain to be able to do over 100 in one go but thats bolx when you slow things down and do them properly. when you can do that 30 good ones, move onto Hindu push ups. Remeber keep flexible, never do the same week out week after week.