Sheets for Nuna Bassinet

Hii, I got a Nuna Demi grow bassinet and stand as a hand-me-down, which I plan to use for the baby’s main sleeping bassinet in our room until they are ready for a mini crib. It comes with a mattress and mattress liner but what about sheets?

Am I supposed to buy sheets or does baby sleep on the mattress liner alone? If sheets, which ones can I use? Nuna website doesn’t seem to specify anywhere or sell this. Anyone know? Thanks!!