Sorry, I tried so very, very hard to read your details and check out your links and it was all too much. It’s kind of late, maybe I shouldn’t even be answering this but I do know that Ikea bed frames, day beds, all of them, are designed for Ikea mattresses and Ikea mattresses do not have the same dimensions as standard twin, double, full, queen and king mattresses do. I ran into the same problem. There was a full size Ikea bed/bed frame that I really liked only to discover that it wouldn’t take a standard full size matress that I wanted to use. I had to kind of abandon the idea of getting the Ikea bed unless I wanted to use their mattrasses. That was a couple of years ago. Maybe things have changed, I don’t know.