Hi spyle,
You may be getting caught up in a lot of the hype and misinformation that is common all over the internet about natural vs synthetic rubber, the Talalay method of production vs the Dunlop method of production, and the “safety” of different types of latex.
There is more information in post #6 here and the posts it links to about the different types of latex but the truth is that all of the latex you are likely to encounter (whether it’s Talalay or Dunlop or uses natural or synthetic rubber or a blend of the two) has been tested for harmful substances to the same testing criteria (usually Oeko-Tex standard 100). You can see the testing criteria that is used here.
Different people may have different preferences between Talalay and Dunlop because they feel and perform differently (see post #7 here) but not because one is inherently any better or worse or “safer” than the other.
There are also some people who prefer organic Dunlop (there is no organic Talalay) over 100% natural Dunlop for personal reasons but this would only be for personal reasons not because there is any meaningful difference between them in terms of purity or performance (see post #2 here for more about organic latex certifications).
The first topper you linked from Dreamfoam is blended Talalay and the ILD ratings they provide you for the topper you choose will be accurate.
The second and third toppers are both 100% natural Dunlop sold by Ultimate Sleep and both are listed at 4.7 lbs/ft3 which is about 75 kg/m3. If the density is correct then they are both unlikely to be between 16 and 18 ILD (you can see some densities for Latex Green’s 100% natural Dunlop and their ILD range in post #2 here).
I would decide which type of latex you prefer based on how it feels and performs in the layer you are planning to use it (comfort layer, support layer etc) and then choose the one that is the best “match” for you and your preferences.
Regardless of which one you prefer you won’t be sleeping directly on the latex. It’s a good idea to have a good stretch cover if you are using it as a topper but even without this you would have your mattress protector and sheets over top of the latex so you wouldn’t be in direct contact with the latex anyway.
Hope this helps alleviate any kind of “safety” concern with any type of latex you are likely to encounter so that you are making your choice based on personal preference and the actual differences between them rather than treating one as being somehow “better” or “safer” than the other.
Phoenix