To make that little part of the world, that is going to be his bed and his playing space comfortable, you need the right combination of a crib that is built with safety considerations in mind, and a mattress which fits in right, creating a cozy cocoon for your baby.
Nowadays, what needs to be taken into consideration while buying items like baby mattresses and cribs, are the principles of ergonomics. It is the science of designing products, taking biological factors into consideration. Modern manufacturers of mattresses are increasingly taking ergonomics into consideration, while designing them.
See to it that the product you purchase has been optimized ergonomically. Mattress manufacturers have to adhere to standard safety precautions while designing cribs and see to it that the distance between slats and the overall dimensions are built according to specifications. This makes sure that the safety hazards posed by past designs are circumvented.
The standard size is designed, by taking the dimensions of a crib into consideration. Most manufacturers advertise that their cribs are built to fit the standard specifications.
There are two main types of crib mattresses, according to the material from which they are built. They are foam and coil mattresses. Foam-based ones have a thickness in the range of 4 to 6 inches, while coil mattresses have a thickness range of 5 to 6 inches in general.
The numbers you need to keep in mind, while buying a mattress for the crib to remember the standard size is 51.625" x 27.25". While selecting the mattress, buy the crib before, so that you have an idea about what will be the right fit.
To test whether the mattress is right for your crib, lay in the mattress inside and see how much space remains between the crib rails and the mattress. If the space is greater than the width of two fingers, then the size is too small. If you can't test directly in a crib, make sure that you have its measurements with you.
Then, measure the mattress dimensions to get an idea about whether it's a right fit. The standard size of a crib mattress is such that it can serve as a baby bed and later also serve as a toddler bed as he/she grows up. So, you don't need to buy a new one that soon.