Our 5yo is still not 40 pound. Is there any booster car seat that would fit her? Otherwise how would you recommend to travel with her? We do not want to bring car seat in the flight (even not checking at the gate) and do not trust rental car seats. Maybe buy a cheap one at Costco when we arrive is an idea - but how to get rid of it at the end of our trip? Thanks!

look at the recommendations on carseats for the littles and get a light weight high back booster seat to travel with.

First, you need to check the laws in whatever State you will be in for car seats. Generally, your daughter cannot be in a booster seat, must be in a full car seat. as she weights less than 40lbs, As you must have a separate seat for her on the plane, it would make sense to take the seat you have, if it's approved for use on planes, with you and let her sit in it on the plane.

If you're going to buy "a cheap one at Costco" why not "trust" the rental car seats!! How are you going to get to Costco when you arrive with her in the car.

The LAWS OF FLORIDA allow booster seats.

Yes, but just above your highlight
t’s important to remember that car seats aren’t just for babies. Florida law states that children ages 4 through 5 must be in a separate carrier, integrated child seat, or booster seat. There are many five-year-olds starting kindergarten this school year, and while they may not seem like your baby anymore or their peers may be in a different type of child restraint, it’s important for parents to use a car seat that fits their child’s current size and age.

A rental car child seat can still be safer than a booster seat, IMO.

But you won't get arrested for using whatever--in Florida.