When BeagleDaddy and I were first married, the only people we gave the master bedroom to while they were visiting was his parents. They were both elderly and his dad had serious back issues. The sofa bed we had usually put a bar right against the lower back and that would have been agony for his dad.
We don't have a spare bedroom any more so no overnight guests.
A little off topic, but.....
A handy little trick I learned from a friend with that kind of sofa bed was to turn around. Put my feet toward the sofa and my head at the other end. It made a huge difference.
Or, if you're not too tall, lie sideways, parallel with the bar!