Hi technochino and welcome to the Mattress Underground 
Looking for a 10" queen sized all latex mattress. Currently sleeping on a similar sized latex mattress which was heavenly when we first bought it almost 12 years ago. Since then, put on some weight and developed some right sided back pain which wakes me up in the AM. Wife has not have any complaints with her side.
Her, 5’3", 120 lbs, back/side sleeper
Me, 5’9", 220 lbs, start off on my back, wind up on my side, right back pain, use a CPAP for my OSA. Thinking about the following build and was hoping to get some feedback.
Top layer: 3" Talalay, 1/2 soft (her), 1/2 medium (me)
Middle layer: 3" Dunlop, 1/2 medium (her), 1/2 medium (me)
Bottom layer: 3" Dunlop, 1/2 firm (her), 1/2 firm (me)
Sorry to hear your old mattress is no longer comfortable for you both. As you may know, any mattress you choose will be vases don your Stats (height, BMI, sleeping position(s) and any underlying health concerns) and your PPP (Posture and alignment, Pressure relief, and Personal preferences. A DIY latex mattress can be fantastic for customizing comfort layers, if you are willing to put in the time and energy to switch layers around to get the perfect comfort and support levels. If you are splitting the layers, you can zero in even further…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, and should last you for many years.
Another thing to keep in mind is that Talalay and Dunlop latex have very different ‘feels’ - Talalay is considered ‘bouncier’ - the difference can be thought of as the difference between angel food cake and pound cake. You and your partner may prefer one over the other.
As for your questions: the build looks to be subjectively fine; you have a higher BMI but the
medium/medium/firm on your side should. provide enough support for you - make sure your alignment is good: if you are laying on your side, your profile should look the same as if you were viewed from behind when standing.
Was thinking that splitting all layers would allow us maximum flexibility to swap out/customize layers if a layer doesn’t work.
Was looking at LMF or Sleep EZ we can split each layer. LMF is cheaper than Sleep EZ by $700 for the above configuration so leaning towards LMF at that price point.
Both LMF and SleepEZ are Trusted Members of the site and offer quality components and excellent customer service. To keep costs down, LMF does allow one layer exchange within 30 days on DIY products (unlike their 100 night sleep trial for prebuilt mattresses), though they have a very low exchange rate; they are proficient in assisting consumers in finding the right components, so it becomes a matter of rearranging layers to dial in the comfort settings instead of needing to exchange layers.
Trusted Member Mattress To Go has a variety of Leggett & Platt adjustable beds, and Richmond Bedding carries Reverie adjustable beds, both of which are very popular and have models from the basics to fully app controlled, with multiple articulation points, lights, and other bells and whistles. I would make sure to follow the recommended bed bases for your latex layers just to ensure you don’t void any warranty in case you need to take advantage of it.
All in all it sounds like you have a good plan in
mind…with a bit more consideration your build can be ideally comfortable for you both for many years!
~ Basilio