I know this thread is old, and sort of morphed into a discussion on the heating aspect of the mattress that comes standard...but since I'm gearing up for a 10-day trip to Sequoia NF, I was looking through the forum just to see what I've been missing in the last few months and saw this. Thought I would share what I did with the mattress situation.
We tried the mattress topper solution too. While it did add more comfort, it also added more height to the mattress, bringing us closer to the roof of the trailer. The other half kept hitting the roof while turning over at night. It also added a lot of weight, making the access to the storage underneath difficult. I was afraid of what that would eventually do to the lift mechanism there, so we didn't use it that much.
We also discovered, while on a January camping trip in Yosemite, that the mattress topper freezes when it's really cold outside! After the second day, we came back to a mattress that was stiff as a board! It would eventually soften up as the trailer warmed up at night, but would stiffen back up while we were out for the day. It was interesting to have our body heat melt the mattress around us, making an indentation where we slept in the shape of our bodies...
So- after all that- we did replace the mattress. I found a business that specializes in RV and other type mattresses. While they don't have one that is exactly the measurements of the one in our A122bh, it was only an inch narrower. The mattress we chose is only 5.5 inches thick, compared to the over 8 with the old mattress and topper. It's more comfortable than the old mattress, and MUCH lighter, which gives us new access to the storage below the bed! The company was great too. They seem to really care that you are getting the right option for your needs and want you to be satisfied.
Here's a link to the company:RV Mattress | Custom Size Mattresses for RV & Campers
We haven't been cold-weather camping with the new mattress yet, so don't know if I will be sleeping on a board when we do...
Hope this helps anyone on a quest to improve the quality of their A-Frame camping experiences!