Hi lenc,
Welcome to the Mattress Forum!
Youâre very welcome.
For those of us across the pond, that would be about 112 pounds at a BMI of 20.5. While I canât diagnose mattress comfort issues online, as there are far too many personal variables involved and I canât feel what you feel, I certainly can do my best to provide you with some general guidelines that might prove useful.
You certainly chose a good quality and durable material. An 80 kg/M3 mattress core would translated to about a 5 lb/ft3 density. While ILDs can vary a bit, this would generally be in the uppers 20s / lower 30s for an ILD, which most manufacturers consider a âmedium firmâ. Of course, terminology isnât standardized, so this information would be more for comparison purposes.
It sounds as if after a few nights you began to adjust to the new mattress and sleeping surface. There will always be what I term a âperiod of retrogressionâ where you adjust to your new mattress and lose some of your learned alignment from our old sleeping surface, and your mattress will also adjust a bit to you. What you describe seems to be that your alignment was fine (as evidenced by you âsleeping quite wellâ) but then you express a desire for a bit of extra surface plushness, which would be normal when sleeping more upon your side as compared to your back.
A 70 kg/M3 would translate to about 4.4 lb / ft3, which most manufacturers would consider in an upper teen â low 20 ILD range, which would generally be called plush. While this would certainly be softer feeling overall than your past choice, youâd also be sacrificing some support by choosing such a plush product.
To learn about pressure relief and support, there is more about primary or âdeepâ support and secondary or âsurfaceâ support and their relationship to firmness and pressure relief and the ârolesâ of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between âsupportâ and âpressure reliefâ and âfeelâ.
Of course the ideal would be to have both suitable support/alignment and comfort/pressure relief in a mattress (especially in this kind of much higher budget range), but if you have to choose one over the other then I would choose support/alignment. There is some great information in this PHD thesis by Vincent+Verhaer (who is one of a group of researchers that I greatly respect) about the importance of good spinal alignment that clearly indicates that for healthy individuals it has the single biggest effect on the depth and quality of sleep and recovery for healthy individuals. Having proper alignment doesnât necessarily mean that a mattress needs to feel hard like a board, and in your situation you certainly would want some surface comfort along with this deep support.
I canât explain exactly what is happening to you, but your current mattress is not as âsupportiveâ as your first mattress, and we know this by the difference in the density of the foam being less in your current mattress. However, a softer mattress can sometimes feel âfirmerâ because it allows certain areas of your body to sink in more deeply (sometimes too much), placing pressure on other areas of your body that have to bear this additional mass, resulting in a feeling of more âpressureâ, which many people relate as being too âfirmâ. Also, the zoning of this mattress can be playing into your feelings as well and with the less dense mattress it might not be supportive enough for you in certain areas. What you seem to be describing with feeling like youâre being âpushed out of jointâ is common for those sleeping upon a product that doesnât have enough deep down support.
Your first mattress seems to have provided you with a good natural alignment, and a compromise might have been to add 1"-2" of a bit of softer latex on top for when sleeping on your side, but not so much that it would negatively impact your alignment when sleeping upon your back. When you are looking for a softer surface comfort (as you initially stated for sleeping upon your side) changes made to the uppermost layers of a mattress will have the most noticeable and dramatic impact. Changing to the softer latex core did provide an initial softer feel, but it also seems to have negatively impacted your alignment.
All of this is my best âtheory at a distanceâ, but I help it, along with the information I linked, is assistive to you.
Phoenix