You wont find a car seat that will go from birth to 7.

We have a Meridian that is birth to 18 kg (12kg rear facing). When DS2 was due we got DS1 a maxirider which is 8kg up to 26 kg.
The new meridians actually go by height, once they get to a certain height you are supposed to change them over, which for us was around 8.5 months :/ (and we by no means are tall, very average!) the only consolation to that is when the meridian is FF, there are 2 reclining levels, 1 being normal FF, the second being nearly rear facing position when they're actually sitting in it.

It's a good seat, but I really wish we hadve known that the height restriction means we had to turn the seat far earlier than if we had the weight restriction seat because we wouldve tried to get the older version