We are getting a new car so want two new high back booster seats to go in it. I have looked at loads and am now confused about what ones to buy. Do I still issofix? Dd is 7 and ds is 10 but very small for his age, same height as dd 124cm so although he is older is safer in a high back booster, he is also very slim I think his weight is just over 3 stone. Any advice or recommendations would be greatfully received