Another vote for the maxi rider.
Expensive but worth it. Don't know about WA but next year in NSW it's going to become law for children to be restained in an approved seat until they're 7 and not to sit in the front until 12 (due to airbags). We're going straight to the maxi rider because we know it is one of the few approved and therefore we won't have to change when the new laws come in.