Hi Mollye1616,
Some of the suggestions in post #2 here may be helpful.
It can take some detective work sometimes to accurately assess the reasons for any discomfort or pain you have on a mattress but there is more about the various symptoms that people may experience on a mattress and some of the possible causes behind them in post #2 here that may be helpful.
If you have ruled out all the other possible causes and if you are confident that your mattress is too firm and all you need is some additional softness or pressure relief then post #2 here and the topper guidelines it links to should help you choose a topper that has the best chance of success. If you can’t test a mattress/topper combination in person and you aren’t certain whether a particular topper will be a suitable choice for you on your specific mattress then I would also make sure that you are comfortable with the return or exchange policies of the retailer or manufacturer you are buying since this may become a more important factor in your purchase decision.
Phoenix