My daughter will be 4 next week. For our everyday use, we have a Britax Advocate. I love it, but it is massive. We are flying later this month (2.5hr flight) and renting a car (2hr drive to hotel). I am planning to buy a new seat for travel since the Britax is too big for the plane. I want to get a seat with a harness that converts to a high-back booster for when she's older. She's 42inches and right at 40lbs. What do you recommend that is light enough to travel with but solid enough to become our everyday seat when she's ready? I've looked at the Britax seats and the Graco Natalius and they are 25-26 lbs. I don't really feel like lugging that through the airport with 2 kids and a carseat for the toddler. Thanks.