Someone incorrectly posted that you don't have to use the lockoffs on the Britax Bodyguard, but you do, the seat is too heavy. Some people found these lockoff's difficult to use and Britax has recently come out with the Parkway, it has side impact protection like the Bodyguard but isn't as heavy and therefore doesn't have the lockoffs.
If you're not comfortable putting your child in a booster yet, try the Britax Husky. It's a 5 point harness seat rated to 80 lbs (not sure about the height limit) It's a huge seat, kind of like a lazy boy recliner for the car.
HTH