Klesperance,
You may have read this already but just in case you haven’t … post #1 here has the basic information, steps, and guidelines that can help you make the best choices.
A mattress is only as good as the construction and quality of the layers inside it and in the case of Serta and most major manufacturers they don’t disclose the quality of the materials and I would avoid any mattress (even for testing) where there is no way to know the quality of what you are considering. No matter how it feels in a showroom … low quality materials (especially in the upper layers) will soften and break down more rapidly and the loss of comfort and support that goes along with this can happen quite quickly (a few months to a few years) and isn’t covered by a warranty … even if you can no longer sleep on the mattress.
Some of the better options I’m aware of in the Hawaii area are listed in post #269 here. There are also some threads that include some discussions and feedback with various forum members in Hawaii in this thread and this thread and this thread and this thread and this thread.
Phoenix