Hi steve0617, and welcome to the Mattress Underground 
Sorry you have been having trouble finding a
good suitable mattress for you and your wife. A mattress is such a highly subjective purchase…no one can tell you what the perfect mattress for you both would be; it will be a combination of your Stats (height, BMI, sleeping position(s) and any underlying health conditions) and your PPP (Posture and alignment, Pressure relief, and Personal preferences).
You may want to start with basics: as you can see comparing the Mattress Specifications You Need To Know to the Mattress Durability Guidelines, latex is one of the most durable materials you can have in a mattress…you do have quite a few data points and components that have worked for you, but until you get the basics down - finding a suitable supportive mattress at your ideal comfort level, especially at the thickness you want. Your ‘best bed you ever had’ may have been comfortable, but as it lasted less than 2 years before ‘falling apart’ it was not really a good mattress!
Such a thick mattress with multiple ILDs and type of latex - Talalay is a ‘bouncier’ form of latex rubber, while Dunlop is ‘denser’ ( think difference between angel food cake and pound cake) - makes your DIY project - which can already be frustrating with only 2 or 3 layers, in order to ‘dial in’ the right feel and support - that much more complex, but a good latex mattress can provide many years of comfortable sleep.
You might want to look at the offerings if the Trusted Members; I would suggest talking to one of the DIY experts like APM, SleepEZ, [DIY Natural Bedding]or [DIY Natural Bedding](https://mattressunderground.com/list-all/item/diy-natural-bedding ), or a customized modulate sleep system like that from Custom Sleep Technology giving them some info line your Stats, PPP and mattress history, they can assist you in finding the right firmness levels for ideal comfort and support. A DIY mattress has the advantage of allowing ultimate customization, with the caveat it’s’ not unusual to need to do a lot of trial and error. Getting the input of an experienced manufacturer can save you a good bit of stress, time and expense.
If you can give us your Stats, we may be able to further comment on your specific layer and ILD questions. In any case - I wish you great success on your DIY journey!
~ Basilio