I did research when looking for a seat for my lad and bought
this seat for him.
Not cheap though, but damn good. All metal frame and extremely rigid and adjustable in every direction possible with removable cover for ease of cleaning.
One thing I didn't like when looking around was the plastic framed seats, when you grab the back of the seat and twisted it they would flex easily.
Also, it has an anti-submarine base to it to stop the child from sliding out under the belt.