Donate to a Shelter or Church
If you don't have any luck attempting to donate your old mattress to the Goodwill or Salvation Army, you may want to try donating it to a shelter or church. Homeless shelters, women's shelters or even disaster relief shelters may accept your donation of a professionally cleaned mattress. Churches might accept your clean mattress for a mission or other program that helps families in need. If you're unable to find a charity in your area, you may want to reach out to an organization like Donation Town that can help find a local charity in your area that will accept your mattress and may even be able to facilitate free pick up.