Sequoia - Mazi riders ~$300 and Maxi Rider AHR (has adjustable head rest) $350. The 5 point harness needs to be replaced with the Protecta Harness ($50-$70 depending on sales etc) when your child is 18kg. From memory I think there recommended weights 9kg-26kg. Apparently there are new seats coming (or current seats recommendations) upgraded to 36kg to cover new legistation in regards to car seats.

Good luck!