Hi beth819,
I normally use the foundation that the manufacturer recommends or sells that would be suitable for a latex mattress. SleepEz sells what’s called a KD foundation which means that it’s shipped in a box UPS and then you put it together. It’s very simple. They are mostly good quality but I have heard a few stories that a lower quality one slips through from the manufacturer in which case of course it would be replaced. They are good value and much less than most slatted wood foundations.
If you want to research foundations more with an eye to possibly saving a little money in exchange for some research time … then Post #13 here and post #4 here (and other posts it links to) have lots more information.
Based on the ILD’s that they were using … the mattresses you were testing were blended talalay which is by far the most common type of talalay sold. Most people couldn’t tell the difference between this and the more expensive 100% natural Talalay. More information about the differences is here and in post #2 here … but unless you have a specific reason for going with the 100% natural … I would choose the blend.
If you decide on a 3" top layer … then make sure that you check to find out about the possibility of a layer exchange to a 2" layer because layer exchanges normally are only between ILD’s in the same thickness. It may also need a different cover if you change the thickness.
I would talk with SleepEz about their different covers because they would certainly know more about them than I would but I do know they carry 3 different covers. Two of them are quilted with wool and one isn’t. I believe that both of the quilted covers use organic cotton but they use different types of wool but I would check with them to confirm this because they may have made some changes since their website descriptions.
The final height of your mattress would be the height of the mattress (10") plus the height of the foundation (the KD is 8") plus the height of the frame which would put it close to what you have now. If you go with a wire grid frame/foundation combination (some of the links in the posts I referred to) … it is 14" and your mattress is 10 which would give you a total of 24".
It seems you’re getting close 
Phoenix