We also have an Aria stroller...here the brand name is "Peg Prego" rather than "Mommas and Papas" but the same thing. Truth be told ours is still in the box as we have been using our Land Rover as the baby hauler and using a Bugaboo Frog system that is way too big to fit in the MINI.
In the USA the Aria is the only choice I know of..but in the UK Silver Cross makes a new one called the "Compact". Haven't seen it in person but in pics and from what I'm told (by an interested party

) I'm pretty sure it is the stroller I would buy. Heck, I'm still kicking myself for not importing one.
Not that the Aria is a bad stroller...and glad to hear from Paul that his is holding up...but I can't say I'm dying to use it. They are a bit "plasticky" and ordinary. The Silver Cross Compact in contrast is quite stylish IMO. Kicks self again
Wish we could get them here.
If you don't really care if your rig is stylish and just want utility the Aria does fit...and it really isn't that bad (especially if you search out some of the better fabric choices).
I assume you can get the Peg Prego (Mommas and Papas) Primo Viaggio seat?
This is what we had. These are very nice and well rated for safety. Again I fitted it to the MINI...but never really used it in that car
One advantage if you do get an Aria and a Primo Viaggio is you can use them together as a travel system. Although you will be chastised to use the car seat as little as possible...so the little one can lay flat.
Rumor has it Silver Cross is working on a car seat travel system. Rakey will be able to advise.
Congratulations