I just wanted to add, that to counter the infa (trek 8 I think it is) seat issue, they have brought out a new seat called the Infa Comfy Cruiser, which is a convertible/booster.
We have just put DS into his and I really like it. It's alot smaller than DD's car seat, has the 5 point harness, a sun shade etc etc, and turns into the booster seat by taking the 5pt harness out once your child reaches 18kgs. ( it is also supposed to be the safest booster seat on the market)
DS will be 3 in July, is about 13kgs, 98ish cms tall and fits in his seat really well. He will use this seat until he reaches the limits and is out of a car seat altogether.
It's also cheaper than a SNS.