My DS is 4 in December, and he is currently 42" and nearly 40 pounds. I am trying to determine what is the safest option for him. Cost is not as important as safety. He typically rides in a captain chair in our Sienna, so size isn't either. However, I would like additional help with a good option for a second car seat/booster for travel, school field trips, etc. Oh, this is so overwhelming and confusing to me!! Thank you!