So Kira just turned 5 and still so tiney. I'm not sure exactly how much she weighs cause I haven't thought about it until now and her dr appt is Monday. Anywho, we've been using a Britax marathon carseat which goes up to like 65lbs but must have an inch from top of her head to the top of her seat. What carseat should I get next? What is the safest?