Hi Mother of Murray,
Although I don’t know your body type and sleeping positions … you appear to be considerably outside of any “averages” if S/S/F is too firm for you. It may also be worthwhile considering a swap for soft talalay as a top layer which will generally feel softer than the equivalent ILD for Dunlop.
The initial break in and “adjustment” period over the first 30 -90 days or so will make a difference as the layers lose any of their initial “false firmness” and the cover stretches and breaks in a bit as well. Once this initial period is complete then further changes will be much more gradual over the years. It may also be worth reading some of the suggestions in post #2 here that may be helpful as well.
If you are still finding that the mattress is too firm after the first few weeks along with trying softer combinations or following some of the suggestions in the previous link or from Shawn at SleepEz, then your experience would be rather unusual and outside of the “averages” for most people but you may be one of those that needs even softer latex than most people would do best with. Your experience is unusual enough that I would also make sure that you have the soft layers on top just to make sure you aren’t sleeping on a firmer layer.
The first step would always be to talk with SleepEz about your experience though so they can make some suggestions as well but the good news is that you have the option to return the mattress if none of the many options you have available work well for you.
If you end up considering the Bella Sera then I would make sure that you know the firmness or density of the layers you are considering as well to make sure that they are softer than the ones you have now (or try as part of any layer exchanges) or you could end up with the same issues and no recourse since the materials would be the same and the only difference would be the design (number and thickness of the layers) or the softness/firmness of the latex.
Phoenix