Westerman 2.0 Firm Mattress - only lasted 3 years

I paid $5400 for this mattress in Hawaii. After 3 years, it has deep impressions on both sides. I have rotated it four times each year, and it is no longer comfortable. The warranty is 15 years or something but only if you can prove it sags over one and a half inches with nothing on it. They do not send out a company rep, or give any help. Bed Firm where we got it, is no help with this warranty either. The choice is to buy a brand new mattress. So, it cost over $2000. a year to have this mattress which actually started sagging the second year. So beware. We have limited choices in Hawaii when buying a mattress but this is the worst of the 6 I have purchased.