Hi lazopair,
Welcome to the Mattress Forum!
Choose a topper is a common manner in which to customize or add plushness to a mattress that is already providing good alignment but isn’t providing you quite enough surface comfort. There certainly isn’t anything wrong with your reasoning should you decide to pursue that course of action.
I’m not sure what options a dealer might be able to make for you after almost four months, but you could certainly ask. Depending upon what they might be willing to provide, choosing a topper could be a better option for you form both a cost and flexibility perspective.
Deciding to purchase a topper would probably be the most convenient option, and give you the most flexibility overall. In keeping with the theme of your mattress and desire for breathability, a Talalay latex topper certainly would be something you may wish to consider.
There are some good guidelines on how to select a topper in post # 2 here and in post #8 here, and some of the better sources for toppers of which I am aware are in post #4 here. The guidelines presented there should be quite helpful in pointing you in the proper direction, or at least providing options available to you to weigh against what your dealer might be able offer.
Phoenix