When you say regular car seat do you mean the infant carrier style that you take in and out of the car?This is just asking for advice, my baby has just gone one and she is a hefty chunk! She doesn’t fit in a regular car seat anymore as she’s quite tall too, will she be fine to have an upright sitting one? Sorry if you don’t know I’m just clueless on this as I’m a first time mum and don’t drive or anything x
It's safest for them to rear face for as long as possible which is currently up to 25kg. Its legal to forward face them sooner, but it really isnt safe. If you Google "rear facing toddlers" you'll find suggestions for Swedish plus tested extended rear facing seats. Check the individual seat for height/weight requirements and find what works best for your baby/car/finances. My own chunk is 95th-98th centile for both height and weight so went from an infant carrier straight to an Axkid Minikid, and she'll stay in that until 25kg and then will go into a high back booster. If she stays on this line she'll be 25kg at around 4 years, often people have lower centile kids rear facing until 7 or 8 years or even longer.
Also if finances are tight the Joie Tilt is a good seat and will rear face up to 18kg and i believe it's less than £50 at Halfords. It won't take you up to 25kg but will give you a lot longer than an infant carrier for a really affordable price.