Hi gardenguy,
It sounds that you like the higher compression modulus (firming up faster) of Dunlop versus Talalay. Even though your Talalay and Dunlop layers are similar in ILDs, they do have a different feel, as you’ve noticed (the Dunlop will tend to feel firmer than the Talalay). One good way to compare the difference in the manner in which Talalay and Dunlop respond to weight when applied, you could with your current layers place the Talalay on top of the polyfoam core and compare that to the feel of the Dunlop on top of the polyfoam core. Some people definitely have an affinity for the feel of one versus the other.
As you seem to want just a bit more surface plushness, but still good alignment, and a 2" latex choice certainly could be a good option. If you like the feel of Dunlop, adding a 2" piece of something in the mid 20 ILD range could be a good option. You could place this atop the 20 ILD Dunlop that you already have for a bit of a “dominant layer” construction, or if you found that too firm you could place the 2" beneath the 20 ILD Dunlop layer you currently have and see how that works. If you decide to go with Talalay for the upper layer, you already have a good idea that you need to choose a firmer ILD, so the mid 20s would be a good choice there as well. You may prefer the Dunlop, as it seems you desire some initial plushness but then want deeper firmness for alignment. But this is a supposition on my part.
As for zoning, various zoning systems can be very useful and worth considering for people who have more challenging circumstances or sensitivities, body types that are more difficult to “match” to a mattress, more complex medical issues, or who have a history of having more difficulty in finding a mattress that works well for them. There is more about zoning in this article and in post #11 here. You may also want to read post #2 here and post #7 here (latex monozone unique properties). Zoned layers of latex can be found, but it is more common in the cores. Some suppliers for latex layers are listed in this component post.
Phoenix