Hi csufman
Glad to hear you have a plan for replacing your mattress. The Naturepedic Halcyon is, as you say quite pricey, and with a little ‘due diligence’ you should be able to replicate similar. Your DIY plan is sound, The coils, cotton/bamboo cover and the topper will definitely allow more breathability to counter your sleeping ‘hot’. There is more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here that you may find interesting as you embark in your DIY. Both Arizona Premium and DIY Mattressoffer quality components you mention and you can ask them to match the feel of the Naturepedic mattress and they can provide a solution based on your stats(Height, BMI, sleeping position(s) and any underlying health issues) and your PPP(Posture and alignment, Pressure relief, and Personal preferences) so you and your wife can maximize the pressure point relief you want with the air circulation afforded by using breathable materials and possibly a topper; The Talalay mattress topper you propose is a good fit as Talalay is considered more pressure relieving than Dunlop as it provides a deeper ‘cradle’ in the same ILD. Its great you have also tested the Nordic II HDM in person as well, you are getting an idea of what you want and just need to zero in on what feels most comfortable to you and your wife.
As you say, it will be difficult to match what is basically an over $8000 mattress with the Halcyon, but your DIY setup seems to be sound and will be a fraction of the cost. Possibly other consumers can weigh in on your build, as we have a lot of DIY enthusiasts here.
Please let us know your experience with your new mattress once you have spent some time with it.
Basilio