Hi ChoctawNole05,
You would need to know the type and density of all the polyfoam or memory foam (or gel memory foam) layers in the mattress except for the 1" polyfoam quilting layer which isn’t thick enough to be a weak link in the mattress.
To be more specific (from top to bottom) …
1" Performa Plush Quilt Foam: This is only 1" so it’s inside the guidelines of “no more than about an inch or so” of lower quality or unknown materials so you won’t need to know the density of the polyfoam quilting layer
2" TheraCool Memory Touch Gel Foam: You would need to know the density of this gel memory foam layer.
4" HD Ultra Performance Plush Foam: You would need to know the density of this polyfoam layer.
4" HD Ultra Performance Firm Foam: You would need to know the density of this polyfoam layer.
I would suggest 1.8 lbs as a minimum for polyfoam layers yes unless the mattress is in a lower budget range where there may need to be some compromises in the cost and quality/density of the materials and in this case if you aren’t in a higher weight range (more than the low 200’s or so) where you would most likely compress the deeper support layers “through” the comfort layers more deeply than those that are in lighter weight ranges then 1.5 lbs can also be suitable.
While it’s not possible to quantify the sleeping temperature of a mattress for a particular person or know for certain how two mattresses will compare in terms of temperature regulation (there is no standardized testing for this) … there is more about the many variables that can affect the sleeping temperature of a mattress in post #2 here that can help you choose the types of materials that are most likely to keep you in a comfortable temperature range. Your mattress protector and your sheets and bedding and bedclothes can also have a significant effect on sleeping temperature regardless of the type of materials in your mattress.
The layers that are closest to you will have a bigger effect on sleeping temperature than layers that are farther away from you so upper layers will have a bigger effect than deeper layers.
Gel foam materials tend to have a cooler surface temperature when you touch them but the benefits of gel materials tends to be short term so while the gel can help with cooling when you first go to sleep at night, once temperatures equalize then the insulating properties of the base foam material become dominant. There is more about gel foams in post #2 here and the posts it links to.
Having said all that … even though in general terms memory foams and to a slightly lesser extent gel memory foams can be warmer than other types of foam materials … only a relatively small percentage of people that are closer to the oven end of the “oven to iceberg” range will tend to have temperature regulation issues with most gel memory foam mattresses.
Phoenix