Hi sozzeled,
A mattress protector is important with any mattress purchase to protect your mattress against the body oils and fluids that we release each night and keep your sleeping surface in a cleaner and more hygienic condition. It will also protect against accidents and spills and lower the risk of dust mites and other allergens. It will also protect your warranty because even a very small stain on a mattress will void most mattress warranties.
I would tend to avoid a mattress pad which is designed to change the feel of your mattress (see post #10 here) and look for a mattress protector instead which is designed to have the least possible effect on your mattress (unless of course you want to change how your mattress feels).
Post #89 here has more information about the pros and cons of different types of mattress protectors.
Phoenix