Hi Nicky,
I think Daniel covered most of the information about the PLB but I can add a few more comments.
The PLB uses a rayon silica fire barrier which is a completely safe material (see post #2 here).
The glue they use is a water based latex glue which is also non toxic.
Their cover is made mostly from viscose materials which are neither natural or synthetic (they are typically labelled as semi synthetic). There is a little more about viscose or rayon type fabrics in post #11 here.
I would also keep in mind that the mattresses you are comparing are not really apples to apples comparisons (innerspring/latex hybrid vs an all latex mattress).
There are also other examples of both types of mattresses (latex / innerspring hybrid and all latex) available in the SF area that you may also want to compare in post #2 here.
There is also more information about the different types of latex in post #6 here. All of the latex you are likely to encounter (Dunlop or Talalay using natural, synthetic, or a blend of latex) has been certified for harmful substances and offgassing by OekoTex standard 100 or other similar testing protocols so I would consider all of them to be “safe”.
Phoenix