T@B 400 mattress size

We bought a 2 inch thick queen gel topper 79x59 and trimmed about 3” - 3 1/2” off the width (79x56), and just a bit off the corner below the counter fold-down shelf extension.  Seems to fit perfect. 

This is the one we got.
https://www.amazon.com/dp/B07KRXGVFY/ref=cm_sw_em_r_mt_dp_U_NCH3CbTHGKPK4

I’m not sure which sheets my wife bought, but she’s pretty handy around fabric (understatement) and added a draw string to the fitted sheet which stays nicely.  Still a big pain in the tochus to make the bed trying to tuck the upper sheet and quilt top, but nice once it’s put together.  I have slept very well each of the 8 nights we’ve spent in it since we got the trailer in March.