You do not need a slatted bed base if you have a box spring. When you purchase a mattress, you choose either a slatted base or a box spring as the method of support.
Use a slatted bed base for your foam or futon mattress. Use a box spring for your traditional, inner-spring mattress. According to design expert Yanic Simard, a slatted bed base does not have a center support; it only has horizontal slats. The lack of that support shortens the life of the typical mattress. A box spring provides the support that an inner-spring mattress needs, and it extends the life of the mattress.