Done!
26 slats with 2 screws each, all had to be screwed in individually.
I have never been more thankful that I bought an electric screwdriver last year.
That mattress has expanded to be about 4 or 5 times larger than the box it came in, I reckon.
It has springs underneath & memory foam & supposedly also a cooling gel layer on top (very desirable for my menopausal self).
I'm supposed to let it expand for 72 hours before sleeping on it, but fuck that.