Hi KSueSmith,
Hopefully you’ve read the tutorial post here.
I’m not so sure this is accurate … at least for most weight ranges. The “weak link” of a mattress in terms of its durability and the useful life of the mattress is almost always in the comfort layers … not the support layers. There is more about this in post #2 here and the posts it links to.
Post #4 here has more about the factors that can lead to healthy sleeping and post #2 here and the many posts and sources of information it links to may be a useful starting point for those who are interested in more detailed levels of research that can help them answer the question “how safe is safe enough for me” with more accurate and meaningful information.
Phoenix