Help with first DIY build

Cross posting from r/Mattress ...

Hello all,

I currently sleep on a King size Tulo MFTF10 mattress purchased in 2018. The base is adjustable. Over the last few months I have had a LOT of back and some shoulder pain waking up. It feels like the firmness is getting to be a bit much for me? Hard to tell exactly. A month ago I purchased a cheap twin 9.5" Sleepy's Rest Medium Innerspring Mattress that I tossed on the floor to try out. I find that when I sleep on this I seem to get a lot less back pain waking up and it's honestly very comfortable for me, though I do toss and turn a bit more. That said, it's a tiny mattress on the floor so perhaps that is why.

I am 6" 1" and ~190lbs and a 100% side sleeper. Wife sleeps on whatever and doesn't really care.

Looking to buy or DIY a replacement mattress. Was looking at the Serta iSeries® Hybrid 1000 12" Medium Mattress and just expecting to replace it every 5 years or so. However, it looks like I could maybe DIY a superior mattress for roughly the same cost, which also enables me to swap out components as needed?

I'd like to keep my existing adjustable base if possible.

Here is my first stab at a DIY setup. I am trying to get a little less firm than my Tulo, closer to the Sleepy's, as I think it may be better for me as a side sleeper.

EDIT 1/2/25 -- Based on feedback here is the new build:

Cover:
Organic Cotton Cover 12" ($235) - I prefer fire retardant material as we use electric blankets sometimes.

Comfort:
2" - 3LB ViscoSAVER Memory Foam Topper ($96)

Support layers:
1" - HD36-R Foam - Standard Mattress ($28)
8" Quantum Edge Elite Bolsa ($384)
1" - Lux R Foam ($36)

Total ~$779