Look for a firm mattress around 6 inches deep. It should be hypoallergenic and free of phthalates, lead, mercury. Depending on the crib you buy you will want to make sure the mattress fits snuggly in the crib with no space between the mattress and the crib sides.
BABYLETTOPure Core Crib Mattress
SEALYPerfect Rest Crib Mattress
