The futon I use helped a lot of issues caused by my side sleeping. By sleeping on a more firm surface your hips and shoulders maintain better pressure points. The flatter surface allows the body to adjust and move during sleep.

The problem with soft mattresses is they are too comfortable for your body. They allow you to sleep in a way that discourages your body from moving around at night. Creating pressure points that become overuse injuries.

Side sleeping is particularly prone to this. On a soft mattress your hips sink in so your weight bearing shoulder digs into the mattress. This causes the weight of your body to get unevenly distributed. Overnight the ligaments in the rear ribcage get stretched. I wouldn't advise to just sleep on the floor but our bodies weren't meant for soft mattresses imo.