Hi pena,
I’m certainly happy to answer any specific questions you may have but the tutorial post would have most of the basic information, steps, and guidelines that I would suggest.
Post #13 here also has more about the most important parts of the “value” of a mattress purchase that can help you make more meaningful comparisons between mattresses once you are down to final choices between “good and good” if there are no clear winners between them (see post #2 here).
Both SleepEz and Mattresses.net are members of this site which means that I think highly of both of them and I believe that they both compete well with the best in the industry in terms of their quality, value, service, and transparency although as you mentioned they both have different options and designs.
They would be the best source of this type of information about their foundations but outside of any specific concerns you may have either one would certainly be suitable for a latex mattress.
Phoenix