Welcome to the forum.
I have not heard of many folks complaining about their Simmons mattress. But, lots of us have been disappointed with the Denver mattresses. I added a 3" memory foam mattress topper to our Denver mattress and that helped.
In some cases, like ours, the bed support was sagging. Some owners strengthened theirs as a DIY project. My dealer replaced the original under bed framing with 2"x 3" lumber.
After those two changes, we're getting a good night's sleep.
Sherm & Terry w/rescues Steve (std Poodle) & Eydie (min Schnauzer)
2015 Jay Flight 27RLS (Camped: 102 nights 2015, 90 nights 2016)
2006 Ford F350 6.0 PSD, Lariat, 4WD, CC, LB, SRW, auto., Camper pkg.