I'm on a fairly firm memory foam mattress, unfortunately. Slowly fixing my sleep posture (long time face down sleeper, this likely screwed me up), but it takes time to condition yourself to accept sleeping differently

This is hugely important. In fact, as I write this I’m lying on a mattress at my dad’s, who I am visiting, knowing my back will hurt tomorrow. It isn’t only about the money, though. The correct firmness for your weight, etc. matter a great deal. Not trivial to pick from a catalogue or even from trying them out for 30sec at the store, though… the one I’m going to be sleeping on tonight might have been more expensive than the one I have at home, but it just wasn’t chosen by me, for my profile.

Having said this: closing in on my 50s, back pain is becoming a recurrent but unwelcome companion (along with its many crappy friends, such as knee aches and poor eyesight)…

You say that like it's the easiest thing in the world. We had a great bed for the last ten years but it is done.

Bought a super expensive extra firm mattress... immediate back pain. Stuck it out for a month, no good. Couldn't return it coz we chose wrong...now I have a stupidly expensive guest bed.

Tried one of the mattress in a box companies who claimed to be one of the firmest available. it was a soggy mess.

Returned. Bought another with a less favourable return policy but half the price...my wife hated it so much that I donated it to the local op shop.

Were on our latest mattress now and my back is absolutely killing me.

It's just impossible to know what will work for you. A quick lay down in the shop isn't going to cut it, but I am sick to death of looking. A real shame the company that made our original super firm mattress went out of business.

You gonna pay for it?