DS is 9 (May20), he is 4' 6 or 7 " and weighs 104 pounds. He fits in the Monterrey (barely)and the Ambassador (again barely). I have thought about a Prospect (even though I would have to buy the whole seat just to use it as a backless). I just prefer him in a highback as long as possible. He has autism and does not always sit right. However, he does not try to get out of his seat, he just slouches really bad and ends up with the belt around his belly. An anti sub clip would be ideal for him, but I don't think the PWSG is going to be wide enough (we will see). I have even considered a Frontier (as a booster), but that is a lot of money, which I really don't have, for a booster. I don't know, but I will have to figure something out soon. I don't know how much longer I can squeeze him into the Monterrey.