Hi acoustictherapy,
Unfortunately your situation is common throughout the industry and I think most consumers completely misunderstand what warranties cover and what they don’t. In general … warranties only cover manufacturing defects and not the softening of the foam or the loss of comfort and support that goes with it (see post #174 here). Visible impressions that remain in the mattress that are less than the warranty exclusion are part of all warranties in the industry … not just Lucid. These are often about 1.5" although they may be more (as in the case of Lucid) or occasionally less.
Outside of making sure that a mattress is a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) … the most important part of a mattress purchase is knowing the quality of the materials inside it which will tell you more about the useful life of a mattress than any warranty (see this article). The foam quality guidelines I would suggest using are in post #4 here. Mattress warranties have little to nothing to do with the useful life of a mattress and are often more about marketing than anything else.
There is more about the Lucid 16" mattress and some of the information I would want to know before considering it in post #2 here. There is also more about some of the cautions I would suggest for any mattress where the materials are made in China or Asia in post #6 here. I also wouldn’t consider any company where there wasn’t an easy way to reach the retailer or manufacturer on the phone.
No matter which mattress you choose … in almost every case the warranty will include an exclusion like the Lucid (although the depth of visible impressions that are covered will vary) no matter which mattress you buy and it’s always much more important to know the quality of the materials that are inside a mattress … especially in the upper layers which are the weak link of a mattress … than to use a warranty as an indication of the useful life of a mattress.
Phoenix