Sagging is a real problem

Like other reviewers, we have had some serious issues with sagging. My wife is extremely petite and her side of the bed sags as much as mine. Saatva has replaced our mattress twice now in 18 months, and it's still the same issue, so it's quite apparent that it's a fundamental construction issue. We're not really sure what to do about this anymore. Even though the warranty is great, it's not of any use to us if the same poorly designed product comes back. If you compared this review to others that have owned their mattress for longer than a couple of months, you'd see the same comments.