[woah]

My posture improved and my occasional back pain went away entirely after I added "roman chair"[1] to my exercise routine. This is a machine at the gym where you lie on a pad a few feet off the floor and your legs are held in place, and you raise your upper body by contracting your lower back. Reading online now that it can be dangerous if you're too gung ho about it, so do it without weights at first. There are also a lot of other lower back exercises like deadlifts, etc, but this one works best for me.

I like dealing with this stuff through exercise because it avoids the annoyance of having to remind myself to sit a certain way or buying special chairs or desks.

[1] https://en.wikipedia.org/wiki/Roman_chair

[another_account]

To add to this, the hyperextension you are describing can be done in reverse too. There is a proper machine for it, called, unsurprisingly, the 'reverse hyper' but they are rare.

Here are a couple of videos showing different ways to do it without the machine

https://www.youtube.com/watch?v=Ef4noCz83A4

https://www.youtube.com/watch?v=3d9_W--eUcI

As with the standard hyper. Start slow, good form without any weight.

Give it a try!