The most important factor when shopping for a crib mattress is your child’s safety. A baby mattress (or the baby/infant side, if you opt for a flippable version) should be very firm. A firm sleep surface can help prevent SIDS and other sleep-related accidents in infants.
According to the American Academy of Pediatrics or AAP, babies should sleep on firm mattresses and out of reach of any soft or plush items for the first year of their life.
Another consideration is the safety of the materials themselves. Natural, eco-friendly, nontoxic materials like natural latex, wool, and organic cotton will ensure that your baby isn’t exposed to potentially harmful chemicals and pollutants that can be present in mattresses made with cheaper, synthetic materials.
Last but not least, look for a crib mattress with some form of nontoxic water repellency to make accidents and spills easier to clean up.