We have a 2022 BL. I ordered a custom mattress from Mattress Insider for the drivers side. I gave them the dimensions I wanted it, and it came in the mail about 3 weeks later. It’s much more comfortable than the stock one.
I replaced the foam on our rig with a foam shop nearby in the SF area. We then determined that the upholstery material stiffness and seams were another cause for discomfort so recovered them with fleece material. HUGE improvements in both cases. Another issue was the mattresses sliding off the slats into the walk way. Used a product Super Grip in a spray can, works great!