We need a car seat, for my daughter who is 3.5yrs, about 1m tall and just over 13kg, so my son can have her old stage 1 seat. Should I get another stage 1 car seat-at what point do these become unsafe, other than by weight? I'm thinking of getting another Britax Duo Isofix. If not which seat should I get as she needs a 5 point harness, but the multi-stage seats seem to get bad ratings in Which? don't they? Does anyone know? MrsBadger? NannyL?