Hi falcor,
The 9" may be an approximation but if there is a 6" core and an additional 1" on either side along with the thickness of the cover on each side it would be “close enough” to make a meaningful comment about it.
As you can see in the guidelines here … there would be no weak links in the mattress because the quilting layers are less than the guidelines I would suggest which is “no more than about an inch or so of lower quality/density or unknown materials in the comfort layers” so this along with the fact that it is two sided would make it a high quality and durable choice.
This I can’t answer for certain for any specific person because each person’s sensitivities and health concerns can be very different but the latex would certainly be safe (all the latex you are likely to encounter would be either Oeko-Tex or Eco-Institut certified for harmful substances and VOC’s) and if the polyfoam is made in North America and/or is CertiPur certified then “most people” wouldn’t have any issues or concerns with this either.
I’m looking forward to finding out what you end up deciding and you are certainly looking at some very good options.
Phoenix