A mattress topper provides support that can prolong a mattress's life by reducing pressure on the springs, delaying any sagging or general wear. Combine a mattress topper with regularly flipping your mattress and you could see your mattress provide full support for longer.
A mattress protector covers the top of the mattress to protect it from transfer of sweat, spills, bacteria, and allergens. Any moisture that goes into the mattress will create a breeding ground for dust mites and bacteria. A mattress protector helps to preserve the life-span of your mattress.