Looking for advice for a booster seat model for our second vehicle older dodge truck (2002 Ram 1500). Our kiddo is 6 and now getting too tall for our other FF seat with 5pt harness. Our problem is the truck does not have UAS latch or headrests in the backseat, does have top tether. Our current car seat is installed with lap belt and locking clip and top tether. I think we need a high back booster because of the lack of headrests but worry about it being not secured to the seat for when it is unoccupied or when kiddo is getting in/out. I also see that many models have the latch. In our main vehicle we have a Diono Radian that converts to the booster seat which is working great. Any suggestions are appreciated. New vehicle not quite in the budget at the moment...