Hi shan808,
Although your mattress will already be past it’s break in period … if your mattress is too firm there there are some suggestions in post #2 here that may be helpful.
If your mattress is still in good condition and there are no soft spots or impressions on the sleeping surface (which I would assume there aren’t because your mattress is still fairly new) then a topper can be a good way to add some additional softness and pressure relief to your mattress.
Post #2 here and the topper guidelines it links to can help you use your sleeping experience as a reference point to choose the type, thickness, and firmness for a topper that has the best chance of success.
I would also keep in mind that the mattress under a topper will also have an effect on how the topper feels so a topper that works well on one mattress when you test it in the store may not work as well on a different mattress that is either softer or firmer or uses different materials.
I would also make sure you are comfortable with the return or exchange options you have (many toppers don’t allow returns or exchanges at all) because only your own sleeping experience will be able to confirm whether a mattress/topper combination is a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences).
Phoenix