Hi Jill71rdh.
It looks like you are in the latest stages of finetuning your mattress and your experience with SavvyRest’s toppers is helpful … they offer two 3" toppers both Talalay (NR) and Organic Dunlop and it looks like you tried their very soft vitality topper which I wouldn’t recommend for a prone sleeper. You may wish to review the guidelines in this Sleep Positions Article so that you avoid hyperextension in a swayback position that can cause back issues. You are correct the difference between a 2" and a 3" comfort layer can be quite dramatic and also depends on a person’s weight, shape, and sleeping positions. Side sleepers will notice it more (they are more likely to go “through” a thinner comfort layer) and feel more of the properties of the layers below it. The thinner a layer is … the more you will feel the properties of the layers below it. Thickness and softness are connected and a thicker topper will “act” softer for most people.
I would certainly follow Ken’s advice and select a 2" latex (or even less) instead of the 3" especially in combination with the plush version of the Ultimate Dreams and your stomach sleeping postition which would need a firmer sleeping surface. Also In your case being a thinner and lighter body type, you could also do better with thinner and softer comfort layers than heavier body types. The topper will add to the comfort layers that are already part of the mattress. You can read some of the topper guidelines in post #8 here that may be useful as a guide.
Yes you would need a separate cover for your topper. While Ultimate Dreams’ cover is zippered it wouldn’t accommodate the insertion of extra 2" latex layer (UD has a 12" cover encasing 8" pocket coil, 3" latex comfort layer and the remaining 1" accounts for quilted wool/bamboo cover).
Dunlop would feel firmer and it is denser than its Talalay counterpart in the same ILD. Blended latex (such as 70% SBR and 30% Natural latex or NR) is not as elastic and resilient as Natural latex and not as stretchy. SBR or blend is more abrasion resistant and can be made more resistant to aging degradation, NR is more expensive than SBR. It really all comes down to your preferences and particular needs. The decision of “what” to choose in terms of either a mattress or the balance between comfort/pressure relief and support/alignment that may be suitable for a specific person is always up to the only person who can feel what they feel on a mattress and best left to personal testing and your own experiences or more detailed discussions with Arizona Premium. Overall you seem to be on the right track with adding a bit of plushness to your mattress but being careful to not compromise the support you need for your prone sleeping.
I’ll be interested in learning about your final decision.
Phoenix