I think Vogue has a moses basket pattern in their baby section.
My friend who has a Moses basket has a "sheet" (pillowcase, whatever....), a bumper, and a matching rec. blanket to go with it, made out of yellow gingham, I think. It was a shower gift from her MIL and SIL with her first baby. I think I'd definitely do a bumper or liner for it in addition to something to cover the mattress. Just in case baby decides to sleep up against the edge of the basket, ya know?
Charlotte, midwife to some awesome women, wife to Jason, and no longer a mama to all boys S ('01), A ('03) S ('08) and L ('10).