Hi stevenabc,
There is more information in post #2 here about “breaking in” a new memory foam mattress that may be helpful and post #2 here has more information about some of the more common “symptoms” that may also help you to identify their underlying cause. Now that you have a “reference point” it may also be worthwhile testing different mattresses using the testing guidelines in the tutorial post to see if you can find a mattress that is more likely to be a better match for you (both in terms of suitability and in terms of the quality/durability of the materials inside it).
I would tend do nothing for the first few weeks if that’s possible so you can see if your symptoms are improving, staying the same, or getting worse and I would rotate the mattress as well so that it breaks in more evenly if one half of the mattress is different from the other.
If after a few weeks you decide that you need some additional softness because the mattress is too firm for you then a topper can certainly be a good possibility. If you decide that the mattress is already too soft (in either the comfort or support layers) then a topper is unlikely to be a good solution (see post #4 here) and exchanging the mattress would likely be a more effective solution.
Phoenix