Hi naro,
Tempurpedic produces their own memory foam and isn’t CertiPUR certified and doesn’t have any specific certifications for harmful substances and VOC’s that I’m aware of. Anecdotally they have the most complaints about their smell and sensitivities to their material (see here) but they are also the most widely sold memory foam mattress as well so some of the frequency of complaints would be the result of the sheer number of mattresses they sell.
The foams in OMF mattresses are made in North America and almost all of the major North American foam pourers are CertiPUR certified (even though not all the mattress manufacturers that use their foams have applied for their own CertiPUR certification) so this wouldn’t be an issue for me in the case of OMF (although you could also ask them to confirm that the foams they use are made by a North American foam pourer that is CertiPUR certified).
The tutorial includes several links to lists of the better online options I’m aware of that include many different types and categories of mattresses (in the optional online step) and one of them is a link to a list of online memory foam choices.
Assuming that the materials in a mattress you are considering are durable enough for your body type and meet the quality/durability guidelines here (and latex in general is the most durable of all the foam materials so durability wouldn’t be a concern with latex) … the choice between different types and combinations of materials and components or different types of mattresses are more of a preference and a budget choice than a “better/worse” choice (see this article). Some people just prefer some types of mattresses or types and combinations of materials and components and others prefer different types of mattresses and types or material and component combinations.
Every category of mattresses includes hundreds (or even thousands) of different designs in a wide range of firmness levels so it’s more likely that the specific mattresses you tried were too soft. If anything there are probably more comments about latex being “too firm” than “too soft” although perceptions of softness/firmness is relative to the person. There are certainly some latex mattresses that are as firm or firmer than most memory foam mattresses.
Latex and memory foam have very different properties (regardless of their firmness level) and feel and perform very differently from each other. There is more about how they compare in post #2 here but the best way to know which type of materials or which type of mattresses you tend to prefer in general will be based on your own local testing on a range of different mattresses in each category in different firmness levels. It would certainly be worthwhile testing some latex mattresses to see how you feel about them.
Phoenix