A firm mattress reduces the risk of suffocation or SIDS (Sudden Infant Death Syndrome) by keeping a baby's face from sinking into the mattress. If a crib mattress feels comfortable to you, it is most likely unsafe for your baby. Babies will quickly adjust to the firmness of the mattress, even if they don't seem to like it at first. Give them some time and be consistent with putting them to sleep in their crib.