AITA for insisting my mattress back after my maternal aunt swapped it without asking?

I (21) live with my mom (52) and maternal grandfather (86). My maternal aunt came to stay with us. While I was out, she switched my mattress with the one in the spare bedroom upstairs, where she was staying. Now, my original mattress was wrecked with busted springs, and it's currently set up upstairs in the spare room, basically beating sleeping on the floor.

I'm a poor student living at home, so I couldn't afford a new mattress. The spare one upstairs rarely gets used, so I couldn't understand why a good mattress should sit unused while I had to sleep on a worn one. I was notified of this swap by a phone call from my mom.

When I demanded they be switched back, my family told me to stop making a fuss, claiming I had swapped them without telling them before (which I definitely did not). I refused to return home until the mattresses were switched back.

Eventually, my maternal grandfather called to tell me they were being swapped back, and I went home. However, my mom was in a bad way, saying these arguments "trigger" her. My aunt walked past me, heading to sleep on the couch in the living room, and said, "Don't speak to me." I am upset that she thought nothing of going into my room and taking these herself.

Keep in mind, the worn mattress was upstairs, but the good one had been on my bed for six months. I live here; she doesn't. The mattress originally belonged to neither of us, but it's more mine than hers. She justified taking it back by saying, "I always slept on it when I stayed here," even though she could easily afford a hotel for one night given her good job until an alternative mattress can be arranged. Also, I have Asperger's and ADHD, and her interference with my bed and space really upset me.

So, AITA for wanting my mattress back, even though my whole family is giving me the cold shoulder as if I've done something terrible? Additionally, my grandfather offered me his bed for the night to try and keep the peace, an offer which she would've happily seen happen.

UPDATE: I was just informed that the swap was happening, no one asked me at all. The mattress has been in my house for years, and I pay my way to live here. She is a visitor and the mattress has been in my room for 6 months as my bed. Im really considering getting a lock on my door as I feel that my bedroom should be my space