Hi jaba,
The first step would be to decide on whether you believe your mattress is too soft or too firm and the first place I would start is by talking with the store you purchased from so that they can provide some guidance based on their years of experience with their mattresses and with other customers that may have had issues that are similar to yours and let you know about the options they have available to make any changes to your mattress that may be necessary.
There is also more in post #2 here about the more common symptoms that people may experience on a mattress and some of the possible reasons for them that can also help with the “detective work” that may be necessary to decide on the best potential solution for any issues you are having.
There is also more in post #2 here about mattresses that are too soft and in post #2 here about mattresses that are too firm.
A topper can certainly be helpful if your mattress is too firm and you need some additional pressure relief or softness and if you decide that this is the most likely cause for your “symptoms” then post #2 here and the topper guidelines it links to can help you use your sleeping experience to decide on the type, thickness, and firmness of a topper that may be helpful.
Phoenix