Hi John Smith,
You’re certainly right about this and mattresses that were made that long ago tended to use higher quality materials (in the comfort layers especially) than the mainstream mattresses made today (see post #3 here). I can also tell you though that if you tested the materials in your mattress for ILD (firmness/softness) that the foams would have lost some of it’s height and firmness since you purchased it even if the foam doesn’t have any visible impressions. If you were to open up the mattress you would probably also discover that the foam inside had some minimal compression but not enough to make any meaningful difference in comfort or support. If your mattress was two sided (which were also the norm at that time) then if you flipped the mattress on occasion it would also even out any impressions and allow the side that wasn’t in use to recover and even though it would still be gradually softening over time, it would soften more evenly over the entire surface so it wouldn’t be as visible.
Good quality latex will be similar. While there may be some slight impressions (that you may or may not notice) … if you choose a latex mattress that is a suitable match for you in terms of PPP and isn’t too soft then it will last you for many years. You can see a video here of a latex mattress that was in use for almost 50 years (although most people wouldn’t keep any mattress for nearly that long because their own needs and preferences would also change over time and 50 years for any mattress isn’t a realistic expectation) and both blended Talalay and 100% natural Dunlop have a long history of lasting decades (see post #9 here).
While it isn’t possible or realistic to expect any foam material to maintain it’s original specs indefinitely or for no changes to occur over time (this isn’t scientifically possible and never has been) … there are still good quality mattresses (such as latex) whose useful lifetime can realistically be measured in decades.
Phoenix