We purchased a standard Omni Pressure mattress for our wide gurney a couple of years ago. Pt report for those that we were able to compare pre/post new mattress found it a lot more comfortable. We do have fewer complaints about the mattress now than we did years ago. We still have some with back problems that have issues, but I'm not sure any mattress would for them. As far as reducing risk for pressure ulcers, the mattress should help, but I don't have any data to give you on that question.
Downside - they're expensive.
Our plan when we update our chamber in a couple of years will be to upgrade to the bariatric mattress. I can't afford a $1300 mattress individually, but rolling it into a big purchase won't hurt as bad.
Personal experience side note: I've spent a nite on that mattress & seemed pretty comfortable (snowed in during a blizzard).
Brian Pruss RRT/CHT
Avera McKennan Hyperbaric Medicine