Hi Vicky,
It’s unfortunate that you didn’t find us before you purchase your Sealy and your Simmons mattress … both of which I would generally suggest avoiding because of the lower quality materials they use in their comfort layers which can soften or break down much too quickly relative to the price you paid (see the guidelines here).
There is more about the different symptoms that people may experience on a mattress and the most common reasons for them in post #2 here that may be helpful but you are really the only one that can feel what you feel on the mattress or decide whether it’s too soft or too firm.
If your mattress is too firm but is still in good condition and doesn’t have any soft spots (virtual impressions) or visible impressions and you just need some extra softness and pressure relief (and the foundation under the mattress is also in good condition without any soft spots or sagging as well which can affect the sleeping surface of the mattress) then a topper can certainly be an effective solution. If the mattress does have soft spots or impressions though and you are hoping to use a topper to “fix” it then your results may be disappointing and at best may only provide temporary or partial results and at worst can make some issues worse. The most effective solution for a mattress that is too soft or has soft spots or sagging is to remove and replace the layers that are too thick/soft or that are sagging (or if that’s not possible or practical then to replace the mattress).
If you do decide that your mattress is too firm then post #2 here and the topper guidelines it links to can help you use your sleeping experience as a reference point and guideline for choosing the type, thickness, and firmness for a topper that has the least possible risk and the best chance for success and also includes a link to a list of some of the better sources for toppers I’m aware of as well. Your experience on the topper you purchased may give you some indication of whether a topper will be helpful.
If on the other hand your mattress is either too soft or is sagging then a solution to your issues would be much more difficult but some of the suggestions in post #4 here may be helpful and worth trying before you decide to replace the mattress.
If you decide to replace your mattress and you are in reasonable driving distance then as you probably read I think very highly of Tom and Royal Bedding in terms of their knowledge and service and the quality and value of their mattresses and I would certainly make a point of including them in your research.
Phoenix