That study is about whether thin, cheap foam mattresses (not hi-tech space memory anything) are worse than cotton mattresses.
Also, "need" is a poor measure. Very little we consider fundamental in rich, developed countries is about "need". Take indoor plumbing, running hot water and flushing toilets - do we really need those? There are people alive today that grew up without those (in rich countries), and they did fine.
Yes, a good mattress is a bit of a luxury, but you're spending a third of your life on it, so it's hardly frivolous to invest in good, comfortable one.
Also, "need" is a poor measure. Very little we consider fundamental in rich, developed countries is about "need". Take indoor plumbing, running hot water and flushing toilets - do we really need those? There are people alive today that grew up without those (in rich countries), and they did fine.
Yes, a good mattress is a bit of a luxury, but you're spending a third of your life on it, so it's hardly frivolous to invest in good, comfortable one.