Ok thanks. I'm amazed air mattresses don't come in standard sizes for rtt.
RTTs vary enough in size, and the actual market is so small, that it would be difficult to make that happen, even if the RTT manufacturer was involved. Cutting foam is so much easier, and having to air up a mattress also runs counter to the speed of pitching & striking an RTT.
Another aspect that's hurting your selection is that you really do have a need for the mattress to completely cover the tent floor. When I was looking at RTT mattress options, I considered leaving a foot or so of the long dimension without a mattress, since no one slept on it, and it could act as a porch or gear storage area.
I hope you find a solution. Iirc, I found some traditional air mattresses that were sized about like what you'd find in a home. Maybe something like that would work for your main RTT mattress, and you could add a smaller one at the foot end of your sleeping space, so the difference in how it feels wouldn't be as noticeable.