A box spring is required for support of your mattress and to raise the mattress to your desired height. If your bedframe has enough slats or a platform that is supportive enough for your mattress you will not need a box spring.
You could however put a box spring on top of your slats or platform if you require additional height. If you have a bedframe that is hollow in the middle or does not provide enough support to distribute the weight of the mattress, you will require a box spring.
Many times, an old box spring will outlive an old mattress. If your old box spring is in good shape and it is not broken, you can go ahead and use if with your new mattress!
