Hi arturob,
The first place I would start (if you haven’t read it already) is post #1 here which includes the basic information and guidelines you will need to “arm yourself” for mattress shopping.
Because of your greater weight … you will need to pay particular attention to making sure that you have good support/alignment on a mattress as well as high quality materials so that you will have a reasonable expectation of good durability. I would tend to avoid 4 lb memory foams (except in very thin layers) or layers that are too soft and thick which would have a greater risk of breaking down more quickly for you.
Your body types are also quite different and post #2 here has some thoughts about how to accommodate this. I would also keep in mind when you read this though that “theory” can be helpful but there are so many variables of body type, sleeping position, and personal preferences that your own personal testing will always be more accurate than any “theory at a distance”.
Select foam would be a great place to start if you are looking for a memory foam mattress because they have their own models set up along with the Tempurpedic lineup so you can compare them in side to side testing. They are also completely transparent about their materials which means that you can make meaningful quality and value comparisons.
Besides Select Foam / Brickell mattress … some of the better options and possibilities in the Miami area are listed in post #2 here.
Of course you’re always welcome to ask any questions or share any feedback you may have along the way.
Phoenix