Crib Mattress Recommendations??

Hi! Just got the Harper crib from Giggle, but I'm having trouble figuring out what kind of mattress to buy (I know it has to be firm and fit snugly in your crib). I'm a little hesitant to order a mattress online since I can't feel the firmness or the material. Should I go bargain and get the highly rated one on Amazon? (Forgot the brand..) or should I go high end and get the organic, foam type and buy it in store like from Giggle or BuyBuyBaby? So many choices and decisions!