Yes, there will be a floor mattress.
Only "quibble" is having the step tongues on the top side, Kids ya know!
You’re correct—I should have flipped them over.
Having said this, the rungs are milled from 1-1/2” stock and the grand kids probably don’t weigh 50 pounds.
The way it’s put together, there’s zero racking for the bed or ladder.
The mattress frame is bolted into the frame using brass inserts in the 4 bed legs. There’s a wooden L-bracket screwed into the back of the mattress frame and up into a ladder rung—it’s barely visible in two pictures. The ladder is also secured to the front corner leg from behind. The mattress frame is attached to the back wall through a stud.
And the rails tie the bed frame to the ladder.
I bounced and jumped on it myself and nothing moved.
It’s a brick ch*thouse.