How long will this mattress last before it sags?

We rate durability at 6.6 out of 10, which is honest for this value tier. The 800 pocketed coils of tempered steel resist sag well, but the lighter 1.5 lb comfort foam means body impressions can appear sooner than on a denser premium bed, so expect solid coil support for years rather than a decade of unchanged feel. A mattress protector and rotating it head-to-foot regularly will meaningfully extend its life.