Is mattress donation possible?

I recently went through the process of ordering a bed-in-a-box with a 100 night trial. The one I chose was a bit too soft for me and gave me back pain. The company very generously sent me a firmer model to try instead, which has worked out great and fixed my back problems. I was under the impression (naively, I guess) that the mattresses that are returned to these companies (in good condition, of course) get donated to charity, as that's what the marketing for most of these companies used to say. However, when I contacted the company to let them know I wanted to keep the firmer model and return the softer one, and that I hoped it would be donated to charity, they basically let me know that I could either donate it locally myself or it was going to be trashed.

The mattress is in perfect condition - only used for 6 weeks, had a mattress protector on it the entire time and has been kept in a plastic cover since it was removed from the bed. But after contacting every charity I can find, including some local domestic violence charities, it seems they all have policies against accepting anything but brand new mattresses. I understand why they have these policies, but it sucks that a perfectly good mattress is going to get trashed because nobody will accept it.

I can ask the company if they'll let me give it away on Marketplace or something (not sure if they'll allow it, but seems better than trashing it) but before I do that, I just thought I'd ask if anyone was aware of any charities that actually wanted mattresses. Is mattress donation actually a thing or was it just marketing waffle from bed-in-a-box companies?