5Pt harness still possible?

My 6.5y.o. son is 70lbs and 52 inches so he is about to outgrow his Britax Regent since the height limit is 53" and he grows like a weed!

So basically the question is "what's next?" Ideally I'd like to keep him in a 5pt harness as long as possible. (I'm getting the feeling that may be unrealistic much longer, everyone else I know has had their kids in backless boosters for 3+ years lol) The seat will stay in the car so I don't care how heavy it is or how wide/large. Safety is the priority.
thank you

At 6.5, I think he would be very safe in a high back booster. You may want to post in the car seat section in the baby forum which gets more traffic.

Is there a reason you want him in a harness? There is a lot of debate between experts if a five point harness is safer than a booster once a child is older.,

I think a 5pt is always safer. But at 6.5 and 70lb I would use a booster without harness. Could he sit still for a 20 minute car ride?