Recommendations for group 2/3 car seat

[Zigster]

When I bought my MY12 XC60 earlier this year, my wife bought a couple of new car seats for our 3 and 5 year old boys - the old ones were getting a bit shabby, not least because my eldest suffers from car sickness! She bought the Maxi Cosi Rodi XP as we've always found Maxi Cosi seats to be very good.

Unfortunately, as our boys get taller, the car seats no longer fit the XC60. The problem is the rear head restraints which lean forward and interfere with the ability to increase the length of the backrest. My eldest is only five (and about 122 cm tall) and already the backrest is as long as it can be as it is pushing against the bottom of the head restraint. He's only going to get taller and the problem worse.

We didn't spec the integrated child booster seats as we prefer full car seats - not just a safety thing but also that the kids are at the age when they still tend to fall asleep on long drives so we wanted the side and head support.

The head restraints can't be removed (AFAIK) so it looks as if we will have to buy yet more car seats! Before I do, does anyone have a similar problem that they have managed to solve - for example, by removing the head restraints? Or has anyone got recommendations for other child seats which don't have the same problem - presumably the head rest on the child seat must move forward to get around the head restraints? I'm assuming the Volvo own brand ones must fit (it looks like they do from the website) - do you know if they are Isofix as the Volvo accessories website doesn't say?

Thanks in advance