DIY Hybrid Mattress Suggestions

I researched a lot into a DIY mattress about 6 months ago and thought I had a decent build, but didn’t pull the trigger then, but now we have finally decided our current mattress is toast. We currently sleep on a Classic Brands Cool Mattress which is memory foam and poly foam. We flipped it over so we are currently sleeping on the firm poly foam side for more support with a 2 inch memory foam topper we got from Foam Factory. It works, it suits our comfort level, but the poly foam is starting to break down and no amount of flipping is really helping anymore.

I’m a 250/5’10 back and side sleeper with a bad back that needs lumbar support. He’s a 290 6’1 back and side sleeper with the occasional stomach sleep who can sleep in almost anything, but sleeps hot.

I already purchased the 8" L&P Combizone coils, but could return them if that was a really bad idea.

My main issue is settling in what to put on top of the coils. I had originally thought about 1/2 inch firm foam for under coils, then 2 inches Dunlop medium for above coils, 1 inch Lux poly foam, then 2 inches 4lb memory foam. Would that be too firm? Do I need more transition?

I was attempting to emulate a big fig originally, but open to any and all suggestions.