We got the Maxi Cosi priori. They say its from 9kg's, but if you read the pamphlet, they also say 9 months! My boy has only just turned 6 months, but already ways 9kg's and is too big for his first car seat. We were really worried about putting him into a forward facing car seat when he is younger than the recommended age, but had no choice really. He sits absolutely fine in it and doesn't flop around at all, the only concern is if we are in an accident, his neck will get hurt.
My SIL recommended it to us as she had one for her daughter which got passed onto her son. He is now 3 years old and still using it. The material where he kicks it is a bit worn, but otherwise its still perfect.
Thing I love about it is that it just fits so perfectly into the car.