I would suggest reading a couple of the articles on the site which hopefully will help you with a few basics about what you are looking for and help with some of the confusion.
First is post #1 here which has all the basic information, steps and guidelines you will need to make the best possible choices.
It also includes a link to this article which will help as well.
Finally this article about the different types of materials in the comfort layers and the different types of support cores will give you some information about the materials that are used in most mattresses.
There are basically 3 different types of foam. These are Polyurethane foam (polyfoam for short), memory foam (also called visco or visco elastic foam or “Nasa foam” among many other names), and latex foam. All of these are just different types of foam and each of them will act and feel different and last for different lengths of time. The comfort layer and support core overviews will give you some idea of the differences between them.
If you want more detailed information about either memory foam or latex foam (the two more expensive foams that are used in a mattress) … this article about the pros and cons of memory foam and this one about the pros and cons of latex should be helpful.
A mattress is only as good as the lowest quality material inside it so its important to only buy a mattress from an outlet which will tell you what is in every layer of your mattress and has the knowledge and willingness to tell you the difference between the materials. The best outlets also have the knowledge and the willingness to show you how to choose a mattress that gives you the best pressure relief, alignment, and feels the best for you. The goal is to find the best mattress for your height and weight, your body shape, your sleeping positions, and your preferences.
The places that are the most knowledgeable and also use the highest quality materials and have the best prices are almost always smaller or mid size manufacturers that either sell factory direct or through sleep shops that have more knowledgeable staff. They are also more interested in helping you find (or will build you) a mattress that is best for you rather than one that is best for their profit margin.
In your case you are fortunate that there are several local factory direct manufacturers in the area that typically make some better quality/value mattresses. They include …
http://www.comfortcustombedding.com/ Plantation. Local factory direct manufacturer that makes a full range of quality mattresses using latex, memory foam, innersprings. Will also custom build.
http://www.demattressinc.com/ Miami. Local factory direct manufacturer that makes a range of latex, memory foam, and innerspring mattresses. Will also custom build.
http://schraderbeds.com/ West Palm Beach. Local factory direct manufacturer that makes a full range of quality mattresses using latex, memory foam, and traditional innerspring/polyfoam mattresses. Are open about the materials they use and will also custom build.
http://www.zenomattress.com/ Ft Lauderdale. Local factory direct manufacturer. I talked with Jim (employee that has been with them for over a decade) and they are 3rd generation manufacturers who custom build using any material including memory foam, latex, and innersprings/polyfoam. Are open about their materials, and have good quality/value and have a range of mattresses on the floor for testing.
Shop Affordable Home Furnishings & Home Goods - IKEA Sweetwater, Sunrise, FL. See post #3 here for some of the better quality/value here.
http://www.nationalfoamproducts.com/ Pompano Beach, FL. Custom Foam mattresses (polyfoam, memory foam, latex).
http://www.starbeddingmfg.com/ Hialeah. I have talked to Gabriel (the son of the owner) and they specialize in wholesale manufacturing to retail outlets in their area and hotels but they also have a local showroom that sells factory direct. They mostly make innerspring/polyfoam mattresses that are better quality and value in low to mid budget ranges. Very knowledgeable and open about their mattresses.
http://www.floridabeddingcorp.com/ Medley. One and two sided innerspring/polyfoam mattresses only
Some of the local retailers that may also be worth considering that may have some good “possibilities” include …
http://www.floridaorganicmattress.com/ (Green Dwellers) Plantation. They are a retailer that carries Savvy Rest, Royal-Pedic, OMI mattress, and WJ Southard latex and latex/innerspring hybrid mattresses including some that use certified organic amterials. These are all high quality mattresses that would be of interest to consumers where organic certifications are more important. They are good for testing different types and combinations or latex but they can also carry more premium prices so make some good value comparisons here.
http://sleepnakedorganicmattress.com/ Retailer in Boca Raton, FL. They sell Savvy Rest, Naturepedic, Organicpedic (OMI), and Pure Talalay Bliss mattresses which are all very high quality mattresses and include some certified organic latex mattresses as well. Once again I would make some careful value comparisons since these can be in higher budget ranges as well.
http://www.aventuramattress.com/ North Miami Beach, FL. Retailer that carries Pure Latex Bliss, Sherwood, Nature’s Sleep who all make some good quality mattresses which may also be worth including in your research (as long as they provide the specs for the mattresses you are considering).
http://mattressxperts.biz/ Fort Lauderdale, Boynton Beach, FL. Pure Latex Bliss Talalay latex mattresses and Savvy Rest component latex mattresses.
http://sleepongreen.com/ Miami Beach, FL. Sleep on Green latex/coir/wool/cotton mattresses.
Bedding Barn - Locations and Store Hours Davie, Tamarac, Deerfield Beach, Boynton Beach, West Palm Beach, FL. Pure Latex Bliss, Jamison, Gold Bond, Symbol
Providing South Florida with quality sleep products for over 10 years... Paisley Furniture Fort Lauderdale, FL. Lady Americana, D’Angel
http://www.heavenlysleepbedding.com/ Boynton Beach, FL. Natural and synthetic latex mattresses.
http://www.citymattress.com/ Boca Raton, Boynton Beach, Wellington, West Palm Beach, Palm Beach Gardens, Jensen Beach, FL. PranaSleep, Lotus, City Mattress, RedBed, SleepLogic. CAUTION: Make sure you can confirm the type and quality of all the materials in their mattresses here before considering any purchase.
http://www.brickellmattress.com/ Miami. Showroom and local store for http://www.selectfoam.com/ . They do carry some good quality mattresses and used to be a member of this site but because of ongoing customer service issues and delays their membership was terminated and I would read the warning here before considering them.
There are a few others that also make factory direct mattresses but they make marine mattresses so I’m including them for reference.
http://www.hmcwest.com/ or http://boatbeds.com/ Ft Lauderdale, FL. Marine mattresses only
Contact Us Fort Lauderdale, FL. By appointment only. Blue Wave yacht mattresses.
Some member feedback about some of these is in post #5 here and a forum search on each of them may also bring up more information.
This should give you some very good choices who not only use good quality materials but will likely have better value than any chain stores or major brands that you would otherwise spend time at or are more heavily advertised.
Hope this helps