Does the Marita come with a mattress?
Do you mean the carrycot of the Roan Marita? That, yes, comes with a mattress - all bassinets normally do come with a mattress included.
If you mean the seat and some kind of cushioning seat liner, that depends, but normally, no, there's no soft insert on the seat. Any universally fitting one should do, however - it just needs to be purchased separately.