Hi noahsi.
Latex ILD rating is never an exact number, it is usually a range. I took the 36 ILD queue from the specs you mentioned they gave you. Generally, different materials including latex have a variance across the surface of the 6" core so in one place it may be … say 34 ILD and in another part of the core it may be 36. the ILD rating is usually an average of the range across the surface. Blended Talalay has less variance (+/-2 or so) than Dunlop which may vary by more (+/-4 or so). 100% natural Talalay can have a larger variance than blended Talalay.
How the latex ILD is given is determined by the manufacturer of the foam (what ranges they decide to produce) or how the reseller wants to advertise it. You can see the ILD numbers and the “word ratings” that Talalay Global (who makes the Talatech blended and natural latex you referenced) here. Talalay Global calls their softest natural Talalay N1, with a range of 14-19.99 ILD. The Talalay process tends to distribute the latex rubber particles quite well due to the vacuum seal/flash freeze part of the process, but natural rubber particles are stickier, less consistent, and more difficult to work with than synthetic rubber, and there can be a bit more slight variation in ILD for a blended versus natural Talalay core, although the range of +/- 2 or so for the ILD is quite standard. The larger variances tend to be with Dunlop, as you can get some more settling of the latex rubber material in those cores, depending upon the process, with a +/- 4 ILD or so being a common variance.
As far as the best ILD for your side of the bed I’d keep in mind that the ILD of different materials or different types and blends of latex also aren’t always directly comparable to each other (see post #6 here) You are going in the right direction by going one notch up on the ILD for a firmer feel if the layer you tried is also Natural Talalay from the same source (Luma’s source is Talalay Global)
This is because using the ILD of a particular layer or combination of layers as a reliable indication of how soft a mattress may feel to you compared to a different combination of layers can sometimes be misleading especially as you are in the stage of fine-tuning your side. I’d make sure to call SleepEz and prepare a short “elevator speech” with the construction and specs you have now (include NR, SBR, or blended), your stats, and a brief history and ask for their experienced input. They do have all latex types in their manufacturing facility and they can match things for you based on your description.
On top of my head, here is a shortlist of returnable toppers sources. Surely there are some other ones on our Trusted members ~ Directory so you may want to have another look.
Naturally Nestled has a very generous free return policy, however, at this time they offer only Dunlop.
Latex mattress Factory has both Talalay and Dunlop with a good 30 exchange & return policy but it has a $45 flat fee to cover a portion of return shipping.
SleepEZ has a similar policy except that customer is responsible for shipping costs.
Luma Sleep as you know also has 2" -3" Talalay toppers with a 30-day In-home trial. I am not sure if they do exchanges for the toppers.
Phoenix