The canopy can usually be moved back to get them easily out and in. If his head is contained within the shell, then he's OK in it safety wise.
The different stages with the weight groups aren't really used any more, only for older seats conforming to an older legislation. At his age, if you want to move him to a larger seat, you'll need one which he can continue to rear face in. There are plenty of these so don't worry :) Most of them start from 61cm which is basically 3-4 months (he should be able to sit with support).
The seats for the next stage come in two different sizes, you've got seats up to 105cm, which is approx 4 years (but if he's 73cm at 6 months, 105cm is likely to be more like 3 years old). These are options like Maxi Cosi Mica, Britax Dualfix, Joie 360 Spin. They can be rear facing up to 105cm (rear facing is safest for as long as possible) but they also have a forward facing option which can be used from minimum 15 months.
You might even have one of these which can go on the base you have, if you have a Maxi Cosi FamilyFix base. However the Pearl range is quite basic, doesn't spin unless you have the 360 base, and commonly doesn't fit children well until they are more like 9+ months old. You might also want to keep the base free in case you have another baby and want to use the baby seat again.
Or you could look for one of the larger 61-125cm seats such as Axkid One, Besafe Stretch, Axkid Minikid 3. They are a bit more pricey but they last longer, up to approx 6yo if again he stays on the same centiles. They are just rear facing, but they are designed a bit better for longer rear facing with more leg room and fitting more compactly in the car.
Outgrowing a seat at 3yo would mean buying another seat before you move him to a high backed booster, so it can benefit to invest more into the longer lasting one in the first place, unless you know you'll need two anyway because you are definitely planning another child.
I would personally not recommend the ones that go all the way up to 12 years and incorporate a booster seat. They take up more space, the harnessed mode is normally short lasting and they don't do as well in safety testing.