Hi Km,
like Km … I would also be cautious about claims of a 20 year lifespan for a mattress because there are so many variables involved in the durability and useful life of a mattress that are relative to the person or the design of the mattress rather than the mattress materials (see post #4 here and the posts it links to for more about durability and the useful life of a mattress).
I would also make sure that you don’t use the length of a warranty as an indication of how long a mattress will last for you (see post #174 here) because warranties only cover defects and not the loss of comfort or support (or changing needs and preferences) and the loss of comfort and support over time isn’t considered to be a defect unless there are also visible impressions in the mattress that are deeper than the warranty exclusions (which is often not the case).
Some of the better options and possibilities I’m aware of in the West Palm Beach area are listed in post #2 here and there is also a list in post #2 here centered on Ft Lauderdale which is mostly duplicate but also includes some options in Miami and has a link to a thread with feedback about some of them.
Phoenix