Could anyone advise me on the best car sat to get for ds. He is 4.5 months old and currently in a britax group 0+ car seat. He weighs just over 9kg and is very long. His feet have been sticking out of the seat for ages and now the top of his head is level with the top of the seat. Am I right in thinking that it is not safe to keep him in this car seat any longer? If so what should he go in next as he is not old enough to move into the next stage? Thanks.