I don't know if this helps, but I have a 2020 16FQ and I had the dinette ripped out and I put in a jackknife sleeper sofa in that area instead. I'm almost 6 ft tall and when open, I can sleep comfortably. I would describe it as no more than a full size bed at best. Sorry, I don't have the measurements. That said, with the sofa bed open you won't be able to easily walk through the narrow aisle to get to the bathroom as a result. Not a big deal for me. But alas, I re-read your question and you are not replacing the dinette you are just trying to put a bed in there. Sorry...
Nissan Frontier 6cyl, 4x4 (2016)