Before buying a crib mattress for your baby, it is always recommended to get a little research done on the subject. Amongst others, there are many reputed manufacturers like Colgate, Dream on me, Natural Mat, Naturepedic, Priva Snoozy, Pure Rest Organics, Sealy and Simmons to name just a few but one cannot tell the quality of a mattress simply by looking at its cover.
Therefore a visit to the nearest store is a must. Try to find out the price range and the components that are used in making the different layers of each brand so one can have a feel of each product and choose the right one for the baby. It is always good to choose one which slightly feels hard so that it throws back on you though as adults we prefer softer ones but in case of a baby, the converse holds true. There might also be some case in which the store might want to sell foam or an innerspring one more aggressively over the other. This hardly holds any ground because with time and considerable research having gone into the making; both types are as good as the other.
If you are searching for online reviews of the product, it is always beneficial to get some comments and be in touch with some parents about the product which they have bought. This way, one can get the perfect views from them and plan accordingly as per the requirement.