Hi Toto,
The Beautyrest specs you listed don’t say anything about the softness or firmness of the foam and softness and firmness is also very subjective and depends on many variables so there is really no way to know outside of your personal experience how a mattress will feel and perform for any individual. In general though the foam layers in their plush firm models are the same as their “plush” models but the innersprings are a lower gauge and firmer.
In “theory” … the mattress itself along with a 2" 19 ILD topper should work well for many people with your body types “on average” but clearly it isn’t working the way you want it to for you. In cases like this when “averages” don’t seem to fit I would tend to go by symptoms and personal experience rather than by theory because there is no certain way to predict how any combination will feel for any individual outside of their actual experience.
I would also make sure you have ruled out any other possibilities other than the mattress and topper itself (see post #2 here) that could be contributing to the firmness of your mattress and whether anything else is contributing to the firmness of your mattress or the pressure points on your shoulders. I would particularly look at your mattress protector or any mattress pads on the mattress and the thickness of your pillow (which can also lead to pressure or discomfort in the shoulder area).
There is also a possibility that your sleeping position (such as sleeping on an arm or a position that restricts circulation) is causing your shoulder issues rather than the actual topper/mattress itself because your mattress/topper doesn’t sound particularly firm to me and again “in theory” wouldn’t normally lead to shoulder pressure points.
If you have ruled out any other factors … then I would use the topper guidelines and your actual experience to add to the thickness of the topper (either as a replacement or as an additional topper layer).
Keeping in mind that neither of the options you listed includes the effect of the top 5" of your mattress (which isn’t known) … as a general rule if you are uncertain and choices appear to be fairly equal I would lean towards slightly firmer rather than softer and slightly thinner vs slightly thicker so that you have less risk of replacing a pressure issue with an alignment issue (which is worse).
In most circumstances I would also tend to avoid latex in the 14 ILD range in combination with what is already fairly thick and soft comfort layers if weights are average and up although it could work well for some people. It may also be worth considering adding another 2" of 19 - 24 ILD as a middle option under your 2" of 19 ILD (and I would probably tend towards 24 because it’s still in the soft range but slightly firmer) which would be firmer and less risky in terms of alignment than your softest option but softer and less risky in terms of pressure relief than your firmest option. My concern would be that you were “jumping over” the layering that may be best for you but again only your own experience and to some degree trial and error can know for sure.
Phoenix