For safety reasons you shouldn’t be putting any extra mattress in the bassinet, the upper position of the mattress. When you not longer use the bassinet and want something softer, dream on me 3′ pack n play mattress is perfect for this playpen. You can buy it on amazon.
It does NOT come with sheets. Graco’s pack n play fitted sheets will fit the play yard. Most of the pack n play sheets from other manufacturers will work fine.
It comes with a thin foldable mattress that fits the pack n play. The mattress is fine for an infant to sleep on and will be fine for playtime as well. Even the doctors will tell you to sleep your child on a firm surface on their back. All you need is sheet(s) and or a blanket.
However, keep in mind that the napper and changing table must be carried separately. The napper collapses flat when used outside the pack n play, just like a blanket.