Can anyone point me in the direction of information regarding the safety of a 5 pt harness versus high back boosters? My child is 6 years old, weighs 48 lbs and 46" tall. We recently moved to Spain. I am having a hard time finding seats that allow for a 5 pt harness for an older child. It makes me nervous watching hbb crash tests how much child moves - a harness and tethered car seat seems to not move as much. Thanks!!