Lit superposé simple au dessus d'un lit double Akyiah Kids

Here’s the thing. It says twin over twin, so you expect two twin mattresses, right? Wrong! The bottom mattress needs to be about a foot wider than a twin. I assumed (mistakenly) that the photos were showing a twin/full variation sine it said twin over twin multiple times in the Desi and never said the bottom was bigger. It’s put together (took us a good 6 hours since some of the holes were not drilled straight/were out of alignment) so we’re keeping it, but now I need to find a piece of 10x12x76foam to cover the space where the slats are bare. On the plus side, it is nice looking and sturdy. The picture shows a twin-sized mattress.