Hi FeveZs,
Based on some of the feedback I’ve seen … Gardner tends towards firmer mattresses although of course firm and soft is relative to each person.
Like all mattresses … a latex mattress will have an initial break in period where the foam will soften slightly and the cover will stretch a bit which will give a softer feel to the mattress. There could also be some other factors that are contributing to the firmness of the mattress and there are some suggestions that may help in post #2 here. One of these is to make sure that your mattress is on the same base or boxspring that you tested in the store because with a 6" mattress the boxspring or foundation that it’s on will make a difference.
Which of their models do you have and do you know the details of the layering?
Regardless of which mattress you have … it would provide a great base for a topper if you need some extra softness because there are no low quality materials in the mattress. Latex is a very high quality material and most people only need somewhere in the range of 6" to 9" depending on their body type, sleeping positions, preferences, the thickness of the comfort layers they do best with, and on the type of base under the mattress. The idea that thickness relates to the quality of a mattress is really a myth promoted by larger manufacturers who use it to sell a lot of low quality foam or pillowtop mattresses to consumers that end up breaking down and softening much more quickly than they should. You can see an example here of a relatively thin latex mattress that was used for over 40 years.
I would first give your new mattress some time (30 days or so unless this is just not practical) both to go through any initial break in period and your own adjustment to a new sleeping surface and then eliminate the possibilities one at a time. If you do decide that you need a topper then post #2 here and the guidelines they link to (as well as your own testing of toppers on the same mattress with toppers at Gardner) should be helpful.
Phoenix