I know every baby is different but wondering if you've thought about switching over to a convertible car seat yet? Or thought about when you might? We use the Chicco KeyFit 30 carrier/car seat and I've been researching when to switch, I've found so many confusing answers am all worries when to switch/when I'm supposed to! Do yall know the rules? Or a website for help on this? She's on the last slot for the straps and her feet are starting to hang over, but her head is not over. She weighs 18 lbs.