Hi wildbeestly,
Christeli doesn’t have a return policy … only an exchange policy (you would pay any difference between the Versailles and the mattress you exchange for) so your options would either be to exchange the mattress for a different one or to add a topper.
As you mentioned the Christeli uses high quality materials so there would be no issue with durability but of course it doesn’t help if you have a long lasting mattress that isn’t comfortable for you.
I’m not clear exactly what you are hoping to change about your mattress outside of the “feel” which is very subjective and if your mattress is providing good pressure relief and you are sleeping in good alignment then I would be quite cautious about making any changes that are too much. The best use for a topper is if a mattress is too firm and you need some additional softness and pressure relief. If you add a memory foam topper then it would also change the “feel” of your mattress of course because the layers that are closest to you are the ones that you feel the most and you would be sleeping directly on the memory foam topper which would be different from the upper layers of your mattress that you are sleeping on now. A memory foam topper wouldn’t have the quilting that is in your cover and would probably have a slower response and less resilient “feel”. The risk of a topper that is too thick or soft though would be that it could compromise your alignment so the best approach for a topper is usually “just enough” in terms of thickness and softness.
If you are looking for some additional softness or pressure relief (or even using a thin topper just to change the "feel) then post #2 here and the topper guidelines it links to has more information that can help you use your sleeping experience as a reference point and guideline to help you choose the type, thickness, and firmness for a topper that has the best chance of success.
Outside of adding a topper … each of the Christeli mattresses also lists a Tempurpedic model that it’s comparable to (the Versailles for example is an approximation of the Tempurpedic Contour Supreme which is their firmest mattresses) so if you test the Tempurpedic lineup and find a specific model that works well for you then you would have a good idea and reference point for which of the Christeli mattresses would be closest to the Tempurpedic that you prefer. As they suggested in the previous reply I would certainly take the time to call and talk to them about the options that are available to you.
Phoenix