The size or dimensions of your perfect mattress greatly depend on the person or persons using it. If you are single, you might like a twin or full size mattress. For a couple you will want at least a queen size mattress, but more than likely a king size mattress.
Keep in mind, the size of your room and the amount of space allocated for your bed. It is always a good idea to measure your space before deciding on which mattress size is perfect for you. If you are looking to decorate your room with end tables and other decor make sure to accommodate for those in your measurements.