Pole vaulting from inside an egg shell

After 2 1/2 years this mattress has become like sleeping inside an eggshell! The center of the mattress sags so much you have to gather up steam to get out of bed, like a pole vaulter. I was happy with the mattress for the first 6 months, but it has gotten increasingly (and rapidly) worse to where I am looking for a replacement. I wake up daily feeling like I've been beaten...achy, tingling arms, sore knees and back. I have friends who own an Omaha Bedding mattress and love theirs. Am hesitant to go through the warranty hassle if I will end up with the same result. Previous mattress lasted 20 years (another manufacturer). Very disappointed.