A couple months ago when I finally had the plan settled in my head I ran out to the barn and grabbed all of the materials I needed.
I grabbed the last of the 12 foot decking boards I had leftover from my deck build and hauled everything down to my basement workshop. I barely had enough material so you can see, looking at the backside of all three sides of the bed, that I actually ran several of the decking boards short to save on wood.
Looking at the “right” side of the bed you can’t tell as everything is hidden behind the 2x6s I used as supports and for screwing it all together. The entire bed frame is 76×80 – the exact dimensions of my king size mattress.