Hi Martina,
This sounds like it is a mattress encasement/protector which has a semi breathable waterproof membrane. They can can reduce airflow and increase sleeping temperature.
Is this an actual mattress cover (that surrounds the layers inside) or a mattress pad? If it has a synthetic fill material such as polyester fibers then this can also contribute to heat issues. Depending on the fill material or batting as well it can also reduce the ability of the latex to contour to your body profile.
Assuming that both of these are surrounding the latex layers the first thing I would check is the effect of removing the protector with the membrane as this is the most likely “culprit” or at least the layer which is having the most effect on temperature. Synthetic sheets can also make a difference. You can see some of the factors that together can affect sleeping temperature in post #2 here but many people have found that removing a membrane type of protector can reduce sleeping temperatures to within “acceptable” limits.
Replacing the mattress cover with a cooler type of cover (such as a wool quilted cover) or adding a wool mattress pad would probably also help but I wouldn’t replace the cover until you have first made sure that other less costly changes don’t work well enough.
All materials will soften slightly at the beginning and there can also be some adjustment period as well. This is generally under a month but it varies with each person and lighter weights may take a little longer. If things are improving after two weeks but still "not quite there) then I would wait a little longer. If there is no sign of improvement at all then it may be worth experimenting with other changes past about the two week point.
[quote]Q5. It may be possible to switch the bottom layer from 36 ILD to 28 ILD. I chose 36 to ensure we won’t have alignment issues. Is it possible that 28 would be firm enough for our weight (we weigh 126 LBs and 130 LBs)? If so, again, how long should I wait before changing the base lawyer. (I believe we have about 1 month from purchase to exchange, probably with a fee.) I am hoping somehow we won’t have to exchange the base layer, partly because we won’t know if 28 may be too soft.
Q6. What is the possibility that we will have alignment issues if we switch to 28 ILD? (I would rather not take any risks on this front.) Under the toppers will be solid wood floor.[/quote]
I would experiment with removing both the protector (especially for heat issues but it could also be creating a “drum” effect and interfering with the contouring of the latex) and I would also experiment with removing the mattress cover as well to see if sleeping more directly on the latex improves the contouring of the latex.
I would try other options before experimenting with changing the base layer although lighter weights improves the odds that a softer base layer will work for you.
I would first make sure though that the underlying cause of your issues are that the mattress is too firm rather than too soft because if the back issues are from the mattress being too soft then reducing the ILD of the base layer may make it worse but if the mattress is still too firm with the layers you have and none of the other options works well then it would make sense that reducing the ILD of the base layer may help.
Your own experience along with “educated” trial and error is really the only way to know with any certainty.
Phoenix