Hello!
The Cybex Aton 5 is a safe Group 0+ car seat and is indeed an excellent choice for your Mamas&Papas Sola 2 MTX.
Talking about the reclining option - the Cybex Cloud models are reclinable. They may be a good option, but realistically, only for families who travel frequently and need a car seat that they use it for their baby even outside of the car a lot. They can then (only outside of the car) recline the car seat flat, so the Cloud provides a safer and healthier environment for the baby. It is not advisable to keep the baby in a partially reclined car seat for a long time, that is why such a feature was designed.
On the other hand, if you are making long journeys regularly, a during-journey reclinable car seat is almost inevitable, or at least a very efficient, child-friendly solution. However, such car seats are only produced by the Kiddy brand (like the Evolution Pro model). Something to consider only if you are on the go very often and for a very long time. In other cases, I am sure you will manage with a regular car seat.
My personal favorites, apart from Cybex, are Maxi-Cosi car seats - my sons preferred the angle of these car seats the most. They are also super lightweight (lighter than Cybex car seats, which you will appreciate when moving the car seat between the car and the flat/house). What's more, Maxi-Cosi car seats are also more spacious (the Maxi-Cosi Cabriofix is one of the most spacious Group 0 + car seat I have ever heard of).