Okay, so this one actually CAN be true.
It depends on what kind of mattress we are talking about.
I would absolutely steer clear of a one-sided innerspring queen set for $399 (or less… Yeah, don’t buy that unless it is for someone you actively dislike).
The issue here is how much foam and of what grade it is on top of the mattress. Usually, these cheaper mattresses have a pillow top and around two inches of polyfoam quilted into the top panel, and that is on top of the pad that covers the spring. Why is that a problem? Over time these mattresses are very prone to body impressions. So what happens when your mattress starts to look like a canoe? That is the polyfoam wearing out prematurely.
HOWEVER — memory foam isn’t the same thing.
High-quality memory foam (not imported knock-off stuff) is extremely durable. It continues to recover from being compressed for years beyond what the traditional polyfoam is capable of.
This is because they are different on a cellular level and memory foam is simply more resilient. Having memory foam on top disperses your body weight so it is distributed over a larger area, which helps the polyfoam lower levels hold up, rather than them taking all of the wear and tear directly.
(TLDR) Do not be afraid of a one-sided mattress if it is memory foam. That stuff is fantastic and holds up for a long time.
As for a Delarkin product, no need to worry at all. All of our mattresses have a 10-year warranty so if I’m wrong fixing it is on us!