Hi stevenkabc,
That’s good news … and at least “one step” in the right direction :).
The density of polyfoam has little to do with it’s firmness/softness and is more related to its quality and durability. Any density of polyfoam can be made in a wide range of firmness levels. There are also several factors that affect how soft a foam feels including the IFD/ILD (which is a measure of how easily a foam compresses), thickness, compression modulus, and point elasticity (see post #4 here). Firmness ratings such as ILD also don’t “translate” well between different types of foam.
You have several options to add some softness and pressure relief to your mattress which includes replacing your current topper with a softer latex topper or adding another layer of foam of the type (either latex, polyfoam, or memory foam), thickness, and firmness/softness that you would.
Post #2 here and the topper guidelines it links to has more information about choosing the type, thickness, and firmness of a topper that may be helpful but there can be so many variables involved in the relative firmness of a material (including everything underneath it) that I would tend to make these choices based on a more detailed conversation on the phone with the supplier of the topper you are considering. Because you won’t really know for certain how well any topper works for you in combination with your mattress or any other toppers you are using it with … the return or exchange policies of the supplier you buy from and the options that you have available after a purchase if a topper you choose turns out to be less than ideal may also be an important part of the “value” of a topper purchase.
Adding thicker/softer layers of foam to your sleeping system by adding one or more toppers can certainly provide additional softness and pressure relief and would be similar to a pillowtop that used the same type and thickness of materials (there are hundreds of different versions of pillowtops) but they would also increase the risk of alignment issues because the heavier parts of your body can “sink down” more before they are “stopped” by the firmer support layers that are deeper inside your mattress. In most cases its best to use “just enough” additional softness to provide the pressure relief you need in your most pressure prone sleeping position so that there is the least possible risk of replacing pressure or comfort issues with alignment issues.
Phoenix