Ds is 3.8 and tall. He is very happy in his Maxicosi Priorifix seat, but I was idly looking at the next size up ones in mothercare the other day when the sales assistant scared the life out of me. According to her DS is far too big for his seat and we need a new one NOW! Have just looked and he is over the weight(18kg), so need to look sooner rather than later - Any recommendations?