Britax Boulvard fits but I prefer a booster seat anyway. At 3 your son is probably big enough for it. Booster won't mess up the leather of the seat either. We made a mistake and installed the Bouldvard without a pad for a few days. Whatever you get, a protective pad is highly recommended as the seat are more concave than a regular car so the pressure of the seat into the leather is much stronger.