It comes with a fairly thin mat of its own that folds up into the carry case - not really padded enough for everyday use, but our baby has slept on it happily enough (sometimes with a couple of blankets under her). I don't know whether it would take a standard sized mattress, but if it did and you had to carry it round with you it would not really be getting the benefit of its portability.
I didn't purchase another mattress for the cot. Our Grandson sleeps on the Mattress that was supplied with the cot. He has always slept very well on it with no problems.
answered on 14 Mar 2014