This is for my 3 year old. I have the opportunity to trade in his old convertible car seat (having problems with) for a new one for a discount. He weighs 41lbs & is about 40in tall. I was looking into getting him in a harnessed booster car seat. I love how they are bigger and more suitable for him at this point. He seems squished & uncomfortable in the convertible one we have now. Any recommendations?