If his normal chest protector isn't working well enough to make him comfortable, you can check out Evoshield products. They make a plate that molds to your body that may help.
My 12yo son was his team's primary catcher this season. I took him to buy new gear as he had outgrown his old stuff. He ended up picking out an Easton helmet, All Star chest protector, and Schutt Scorpion shin guards. He had his reasons why each was the best for him. He'll take comfort over appearance. (At least they are all the same color...)
He also wears an Easton TorsoTection shirt, which helps absorb impact, while not being bulky. I'm not sure how much it helped him behind the plate, but he sure was happy to be wearing it when he took a pitch off of the hip pad while batting...