Hi Donkers83,
Welcome to the Mattress Forum! 
Congratulations non beginning your DIY mattress process. Just in case you haven’t already, read option 3 in post #15 here and the posts it links to (and option #1 and #2 as well) so that you have some good information about the DIY process.
There’s a bit of information about different sleeping positions in this article that you may find interesting.
[quote]This is what we’re thinking.
6" of the firm dunlop core from sleep on latex
3" of medium
1" of soft
In theory we think this should give us a good combination, being “deep” supportive enough for my larger build/stomach sleeping, and soft enough to cushion her.[/quote]
If this is all from Sleep on Latex, this would be a 6" Dunlop core at 44 ILD, 3" Dunlop at 30 ILD and 1" Dunlop at 20 ILD. The key is finding that balance between your prone sleeping posture and you and your wife’s side sleeping posture, making sure when prone that the mattress doesn’t allow too much “sinkage” to allow poor alignment, but not too hard of a surface comfort to feel uncomfortable on your side. Between comfort and support, I’ll generally recommend deep support, as that has a stronger correlation to time spent in the deeper phases of sleep. You didn’t mention what size of mattress you were considering, but have you considered a split configuration with a different comfort for the left and right side of the mattress? Or is that even a worry that you have?
While the configuration you’re proposing certainly could work for what you’ve described, as you stated, it is quite subjective. Before placing a final order, I would phone Sleep on Latex and see if they have any other suggestions based upon their experience with their Dunlop and people of similar BMIs and sleeping preferences that they feel might be worth considering. They are a site member here, which means I think highly of them, their products, and their advice.
I’ll be interested in learning about what you decide to do.
Phoenix