Hi Passionatefornature,
The first place I would start is post #1 here and the information it links to. The first overview has some ILD information that may be useful for example.
ILD means “indentation load deflection” and as it is typically used it is a measure of the relative softness of a foam layer. It is most commonly used for latex and is very similar (but not exactly the same) as the newer IFD measurement that is usually used for polyfoam. You can read more details yet about ILD and IFD and some of the other foam statistics in post #2 here.
It is also important to note that ILD / IFD is not connected to foam quality in any way and is strictly a “comfort spec” … and can be very misleading if it is used by itself. Density is the most important “quality spec” in terms of the durability of polyfoam and memory foam and with latex the type and blend of the latex is the most important information you would need to know. With latex … density and ILD are very closely connected but any density of polyfoam can be made in a wide range of firmness levels and density and softness are only very loosely connected
It is also important to know (unlike what g1981c is suggesting) that knowing the ILD / IFD when you are testing mattresses locally is not important at all. Good objective testing will allow your body to tell you what you need to know about the feel and performance of a mattress much more than any “comfort specs” which will often do more to mislead than help since most people don’t have the extensive knowledge and experience to have a reference point for what any particular ILD combination feels like. With an online purchase … then ILD/ IFD can play a more important role … especially if you have tested some similar mattresses locally where you know the design details and the ILD’s of the layers which can be helpful as a reference point for an online purchase.
I would also keep in mind that softness/firmness is very subjective and that one person’s too firm can be another person’s “too soft” depending on body type, sleeping style, preferences, sensitivities, and physiology. Your own personal testing and the feedback from your body will almost always be more accurate than any kind of “theory” or “formula”.
In many cases dust mite concerns have been overblown or exaggerated (see here for one example) as a marketing strategy although it is true of course that dust mites (or more specifically their waste products) can be a significant factor in allergies for a minority of the population. Post #2 here has some links to good information about dust mites and methods of controlling them.
The previous link has information about latex and dust mites but there can also be a significant difference between the feel and performance of a latex/polyfoam hybrid mattress compared to an all latex mattress for example (see post #2 here for a comparison). Any different combination of materials and components can have a significant effect on how a mattress feels and performs in terms of PPP (Pressure relief, Posture and alignment, and Personal preferences). In terms of dust mites … I’m not so sure that they would be significantly different from each other if every other factor that could involve dist mites was comparable.
The answer to the question of “how safe is safe enough for me” is also a very complex one and each person may have their own answer that they feel most comfortable with. Unfortunately there is no “one size fits all” answers to these types of questions and each person that is concerned with these issues would need to use their own best judgement. Post #2 here has more and links to more information about this very controversial subject but it may also take you down a rabbit hole of sometimes conflicting information.
You can read more about the different types of latex in post #6 here and post #6 here. The previous link has more information about other natural materials. Blended latex is a combination of natural latex and synthetic latex (Styrene Butadiene) not usually other materials like soy or bamboo.
I don’t keep records of specific mattresses, designs, or layering (it would be impossible to keep up to this in a changing market) so the lists I provide are a way to help you exclude the worst choices and focus on the better ones both in terms of quality and value. Your own research (on the phone and in person) and testing will be necessary to find a mattress that best meets your specific criteria and personal value equation. Connecting with retailers or manufactures that have higher levels of knowledge and experience can also be one of the most imporatant parts of shopping for a mattress because they already know what you would otherwise need to learn. My focus is on how to choose a mattress that meets your needs and preferences rather than suggesting what specific mattress to choose which is not possible for someone to do for someone else with any real certainty. I also don’t keep any records of stores that sell used mattresses and don’t recommend them anyway so for this you would be on your own to follow your best judgement.
Hope this helps.
Phoenix