Hi dnazarian,
Welcome to the Mattress Forum! 
That’s a common comment from people coming here to the site, as unfortunately most online sites choose to focus upon ratings, opinions and subjective stories to tell you “what” to choose instead of providing you objective information about a product that empowers and allows you to know “how” to choose (which you can accomplish by reading the mattress shopping tutorial here.)
I wouldn’t be able to tell you if adding a topper will make your back hurt, but if the mattress beneath is simply too firm but still offering good support/alignment, a topper can be an excellent choice to provide extra comfort and extend the useable life of your current mattress. There is more information about choosing a topper in post #2 here and the topper guidelines it links to. Make sure to read through all of the links, especially near the end of the post with the guidelines of how to select a topper.
Phoenix