Stage 1 & 2 car seat with Isofix?

[MegBusset]

DS2 is about to outgrow his stage 0 seat so needs to go into DS1's stage 1 seat. DS1 is nearly 3 and already it's a bit of a squash getting him into his seat (Maxi Cosi Tobi) especially with his winter coat on! So I'd rather not have to buy another stage 1 seat that will be outgrown in a few months.

The only stage 1 & 2 seat I have seen so far is the Britax Evolva but that's not compatible with Isofix and I'd rather get one that is. Does anyone know if such a thing exists? Or is it safe to put a 3yo straight into a stage 2 seat?

[Lionstar]

Have a look at the Jane Montecarlo Plus. If you don't like the idea of using the adult harness then you can use the Xtend impact cushion up to 18Kg (I think).

Also there is the Recaro Monza Seatfix