Hi ColPanic,
While Dunlop doesn’t always come in specific ILD’s … it would be firmer than soft Talalay of the same ILD and would also be less risky because Dunlop gets firmer faster than Talalay as you sink into it more deeply. In other words it’s more “supportive” than the same ILD of Talalay. Of course the most suitable layering and the risk of a soft Dunlop layer would also depend on her weight, body type, sleeping positions, and preferences. I’m not sure of the nominal ILD of your medium Dunlop layer (Savvy Rest estimates that it’s somewhere in the range of 31 - 39) so anything in the 32 ILD range or less for blended Talalay would likely be softer. Blended Talalay comes in a wider range of firmness levels than 100% natural Talalay. If you prefer 100% natural Talalay (whch is what Savvy Rest uses) then it’s generally denser and firmer than the same ILD of blended Talalay but N3 (about 25 - 30 ILD) or N4 (30 - 35 ILD) or any 100% natural talalay that had a nominal ILD in the same range or less would probably also be softer. Some manufacturers may also have Dunlop that is slightly softer than the 31 - 39 range but a little firmer than the soft range of their Dunlop.
There are many good sources for 3" latex layers (Dunlop or Talaly in blended or 100% natural) and some of the better ones I’m aware of are listed in post #4 here. I would also keep in mind that the “norm” for toppers is that they are non returnable (with some exceptions) so if you are able to test a specific layering in person first it would be a good idea. I would also be aware that if one side of a split layer is Dunlop and the other side is Talalay or if the original Dunlop mold is a different thickness made by a different manufacturer than yours then the 3" layer may also be a slightly different thickness. Dunlop and Talalay also have a different “feel” and compress differently and if they are mixed from side to side in the same layer the difference may be noticeable so many manufacturers hesitate to mix Talalay and Dunlop in the same layer. You can see the ILD’s of the Savvy Rest layers in post #2 here as a reference but because there is such a wide range with their natural Dunlop (and to a lesser extent with Latex international 100% natural Talalay) it would be a good idea to talk with the listed suppliers first to see how much confidence they have with the ILD range of their Dunlop.
There are two directions you could go with this. You could split your bottom layer (an electric knife works well) and then you could put the firmer layer up one level and the medium layer on the bottom and this would create more firmness and support under the soft top layer. you could also buy a firmer layer and use it as a firmer spare to replace your medium middle layer when necessary and this would be firmer yet than using F/M lower layers. I would personally consider the first option first.
When Dunlop is poured in a mold then the latex particles will tend to settle towards the bottom during manufacturing so the bottom of a layer is often firmer than the top. If a 3" layer is cut from the top of a 6" core the it will often be softer than the bottom half of the core. There is also a variance between different Dunlop latex layers with the same “word” rating because ILD with Dunlop is not exact and most Dunlop is manufactured to density not ILD so you may find that one of your medium layers is firmer than the other. There are many types of molds but telescoping pincores (where the holes are smaller on one side than the other) may have been used to offset the natural tendency of Dunlop to be firmer on one side than the other so it may not make as much difference as you would otherwise think. You could test a layer on each side with a heavy object (such as a bowling ball) and then mark how deep it sinks to test the relative firmness of each side (in several places because there may also be a variance across the surface) and this would probably be the most accurate method of seeing if one side or one layer is significantly firmer than another.
Phoenix