DS is 6 months. he weighs 8.5 kg and is really outgrowing his graco infant carseat. we also have a britax club class extra carseat. it fits both front and rear facing and is suitable from birth to about 4 years. we would prefer DS to be rear facing, but can we fit him in the passenger seat rear facing with the britax or does he have to go in the back? there is no airbag on the passenger side.