Hi Q8canuck.
Thank you for your kind words and appreciation of our site. You are certainly making good use of it and have learned a great deal in the process 
and while I am sorry to hear about your past “less than satisfactory” mattress decision, I am glad that you are “determined to get it right this time”.
You are correct that a configurable system is “easy and practical” and offers the user the flexibility to customize the feel of a mattress not only immediately after the purchase, but also in the future, without having to replace the entire mattress. There are versions of customizable systems that use all latex, latex with polyfoam cores, memory foam with polyfoam or innerspring cores, and even versions using only polyfoam. As you discovered this can be especially useful when ordering something online, as it gives the consumer a bit of a “safety net” to be able to replace/rearrange layers if their selection doesn’t feel as they had hoped after ordering. MFC’s Presto is a 10" all natural organic mattress, that has a top- brass zipper cover that will allow you to open and rearrange the 4 latex layers inside for each side in the split king to match each partner comfort needs.
Your understanding is correct that Dunlop and Talalay of the same thickness and ILD won’t feel the same in terms of their firmness for most people because they have a different response curve and compression modulus (how quickly a material becomes firmer as you sink into it more deeply). You can see a comparison between Dunlop and Talalay in post #7 here . It is also true that Dunlop is less consistent in its cell structure (has a wider variety of cell size, shape, and structure) which along with its particle dispersion is what accounts for its greater compression modulus. It also uses more latex in the foam (a higher ratio of rubber to air) and is denser. Dunlop has a different “feel” and performance than Talalay and is less lively or springy but ultimately your own experience is really the only way to know which one you prefer with any certainty. Some people would notice more of a difference than others but generally you will “feel” more of the upper layers than the deeper layers … at least when you first lie on a mattress. This is why I recommend that
Talalay and Dunlop have often been compared to angel food cake vs pound cake. Talalay has a more consistent and even and stronger cell structure because even though there is less latex overall … the cell walls or “struts” are thicker and more consistent. There is a little more about the differences in “feel” between Dunlop and Talalay in post #7 linked above.
These component systems are/have been quite popular for many years, and a quick glance at the members of the site will show that many of them offer such component style systems, as well as other mattress companies who are not site members here. Depending on the manufacturer/retailer these systems can be offered in Talalay or Dunlop only or a combination of both. As you already discovered we have a few Canadian Trusted members who offer All latex high quality great value component style systems
You already are aware and engaged in a conversation with one of our Canadian Experts The Mattress & Sleep Company who is closer to your location and who have all latex Talalay mattress options that you can try.
Memory Foam Comfort that you mentioned with their Presto customizable organic (Dunlop) mattresses another of our Expert Members of the site .
I’d suggest that you call
Synthetic Latex - Styrene-Butadiene rubber (SBR) Latex that is a man-made molecular equivalent of natural rubber Latex (developed during WWII when natural rubber Latex became scarce). Blended Latex is a proprietary blend of natural and synthetic Latex (e.g. 30/70). Latex is blended to optimize the desired attributes of Latex foam rubber for its given manufacturing process and end product. It is less expensive than natural rubber and it is more consistent and durable. There is more about 100% natural and blended Talalay in post #2 here . It is also more difficult to work with to make a consistent firmness so the natural Talalay can be made softer than most Dunlop (except continuous pour Dunlop) but not as soft as blended Talalay. The two different versions of Talalay are very similar in feel and are lighter and more “lively” than Dunlop.
My best suggestion at this point is to determine if you like the feel of Dunlop or of Talalay by visiting one of the stores TAMASC mentioned and to place a few calls along the way or engage some of tour experts on the forum as they would be the best to answer many of the questions that you may have as they are much more familiar with their own mattress designs and materials than anyone else and they can use the information you provide about you and your partner’s body type and sleeping positions, your preferences, your history on different mattresses, and the results of your in-home or local testing to make suggestions based on the “averages” of other customers that may be similar to you. Of course, I’d keep an eye on the options you have available and your ability to exchange layers or the mattress itself or use the other forms of fine-tuning the mattress after your purchase or the return policy may also be an important part of your personal value equation or to offset the risk that can go with any online purchase.
Based on the thought you are putting into this and the care you are taking with all the research you are doing I think you will certainly end up choosing between some great options.
Phoenix