Jane matrix car seat (mattress)

[davidtennantsmistress]

we have this car seat - the one which lays down flat as well, as we'll be travelling to see the inlaws quite a bit & will be doubling up as a carry cot for DB, my question is, it says to use a different mattress for over night sleeps that's ventalated.

does anyone know if A) I would just need to get a moses basket sized matress or if the jane matress that's sold will be the correct one - having brought 3 matresses for the cradle i'm lothe to make the same mistake again. :)