Hi downlover,
I’m sorry you’re still having problems finding a comfortable mattress, but as you mentioned before it is difficult with chronic illness and sensitivities. Are you feeling better and able to get out of the house now?
It does sound as if the topper provided too much surface plushness, which is one manner to negatively impact alignment, and without the topper it seems that you were aligned better, but your pressure point issues are waking you up.
The BME Plush uses 19 ILD Talalay in the upper layer and continuous pour Talalay Dunlop in 32 ILD in the layer beneath that.
That’s the ILD range designation used by Mountain Top foam for their continuous pout Dunlop latex.
All the layers of a mattress actually compress simultaneously, not sequentially, and they will each compress to different percentages of their thickness depending on their position on the mattress, the firmness of each layer, the compression modulus of the material, the thickness of each layer, and the compression force that they are exposed to (which depends on the weight of the part of the body in contact with the mattress and the surface area that is bearing that weight which is constantly changing as you sink into the mattress more or change sleep positions).
While “going through” a layer is commonly used as a way to explain things because there is a different amount of force that “goes through” a layer and compresses the next layer of the mattress depending on the hysteresis of the material (how much energy it absorbs) and on how point elastic the material is (how much compression affects or is affected by the surrounding areas of the layer) … it would be just as accurate to say that you will “feel through” the top layer meaning that you will feel the properties of the next layer down to different degrees. Even the softest latex won’t “bottom out” (meaning it has no more ability to compress because the walls of the cell structure are fully compressed on top of each other) if it is on top of another foam layer and will have the ability to compress more yet even though very soft latex will compress to a much larger percentage of its thickness than a firmer layer. Every layer of a mattress affects and is affected by every other layer in the mattress to different degrees.
The compression of each layer (mainly controlled by thickness, firmness, compression modulus, hysteresis, and position along with a few other specs) are what creates the pressure relieving cradle of a mattress in the top layers which re-distributes weight and pressure on the bony prominences and pressure points of the body while the resistance to further compression of the deeper layers is what “stops” the heavier parts of the body from sinking down too far and putting the spine and joints out of their natural alignment. The balance between the opposing needs of pressure relief and spinal alignment is the main factor behind all mattress design and theory and why different mattresses match the body types and sleeping positions and preferences of different people … or don’t.
In addition to this though, ILD is not the most reliable indicator of how soft or firm a layer will feel. Compression modulus is even more important because very few people actually sink into a layer exactly 25% and compression modulus is the rate at which a foam gets firmer as you compress it more. Latex has a higher compression modulus than polyfoam. In addition to this, latex is very “point elastic” which means that a smaller area can compress with less effect on or resistance from the surrounding area than polyfoam. This is much like the difference between pocket coils that act individually and innersprings that have helicals that join the springs together so that the compression of each spring will affect the springs around it which makes the spring stiffer.
Latex has a lower hysteresis (how much energy is absorbed) and conversely a higher resilience (how much energy it returns) than polyfoam so there are also factors that can make latex feel firmer depending on how much a specific layer is compressed in a mattress. Because of its unique qualities and ability to take on the shape of the person on it (point elasticity) it can feel softer and firmer at the same time and some will feel it as one or the other depending on what they are more sensitive to, their body type, sleeping position, and how they sink into the mattress.
With someone that was a heavier weight that used a softer comfort layer … it would be much more likely that they would feel the firmness of the “stiffer” polyfoam underneath it and the transition between the two layers. This is one of those “counter intuitive” circumstances where using softer foam can actually make a mattress feel firmer. This is one of the situations that can arise if you choose too plush of a secondary “transition” layer beneath your plush top layer, as the transition to the polyfoam core can feel too abrupt.
A “transition” layer of Talalay versus Dunlop might feel better to you, as Dunlop “firms up” faster than Talalay (it has a higher compression modulus for a similar ILD rating), if this is where you think you are feeling you sensitivity. Another option for you, which may seem counterintuitive, could be using a slightly firmer Talalay layer on top with a slightly softer Talalay layer beneath, providing a bit more "surface support’ but still good pressure pint relief.
Unfortunately, there is no formula that can predict with any certainty what type of layering you may do best with that can possibly be more accurate than your own personal experience, as it is a quite complex science as to how all of these layers work together.
With your very specific requirements, I wouldn’t be in a situation to choose a mattress for you, and can only offer guidance as to “how” to choose, and I’ve listed in my previous reply to a link to some of the site members here who are good at assisting people with specific needs.
You can see some of the better topper suppliers of which I am aware in post #4 here. At a quick glance, mattresstopper.com, kttenterprises, sleeplikeabear and foamorder.com all allow for returns/exchanges.
You’re welcome. I’m sorry there aren’t “definitive” answers for your situation, but hopefully the information I’m sharing is assistive to you.
Phoenix
Note added:
I moved your previous posts into this separate thread to be easier for reference for you and others reading through this. Also, one thing I forgot to mention regarding toppers is that many people with sensitivities have had relief with wool toppers, but this does involve fabric and with your sensitivities to creases in materials I don’t know if this is an appropriate avenue to purse.