Do you have a budget? Also be aware that combination seats can be hard to buckle as boosters, so some prefer a dedicated booster when the time comes.
I believe the Britax combination seats still have the highest harnesses on the market, but some have concerns about using them with kids over 40 or 45 pounds based on Consumer Reports testing. They still pass the same required tests as all other seats, so that is a debatable reason for steering away from them. I have also seen the Chicco MyFit recommended for taller kids. They both have features to make installation easier.
Since you'd need to install with the seat belt and tether at your child's weight, you wouldn't get much help from Chicco's nice lower anchor system, but they do put lockoffs on all their harnessed seats, which I really appreciate! Britax has the option of their ClickTight, which can make a seat belt installation easier, or it can be finicky.
I would probably go with the Chicco if the vehicle head rest is removable or out of the way (not jutting over the seating position). I have a Britax because it worked with a fixed, forward-leaning head restraint in my last vehicle.