Does anyone know what mental hospitals are like here?

i was born here but ive never been to a mental hospital before, and i dont have any relatives who have been to them neither. im going to my local psychiatrist next week and i'm thinking of getting myself hospitalised because of borderline/ptsd. everyday is a struggle and sometimes i think of self harm and i always suppress my feelings so it's terrible to survive without proper help. does anyone here know what they're like? are the rooms private? can i have personal belongings like plushies, phone/drawing tablet, coloured pencils, my own clothes? i live in shizuoka so id appreciate recommendations. thank you!! 🙂