I relate to you. I'm so tense most of the time that I have severe anxiety issues and have developed health issues related to being tense all the time ( migraines, sore back/neck, acid reflux etc )

Something that helps me is to give myself a massage. At night, I'll sit in bed and rub my body starting from my feet and going all the way up to my scalp. Even massaging places you wouldn't think of like elbows, fingers and palms etc help!
I like your idea of making a place free of distractions. You could put comforting things in there like a super soft blanket/ stuffed animal, and positive quotes etc. For a while I used to pile blankets at my door, and it would help to block out the sound and create a small sense of safety.
Another thing you can do is get a club or some sort of defense 'weapon' and put it next to your front door. It's odd how the presence of a metal baseball bat in my home makes me feel safer, but it can come in handy.

I'm going to need to deal with this very soon, because I want to get a job so I can move out, and I know for sure it will be hard to deal with when I'm living independently. The worse it gets for me, the more depersonalized and paranoid I get. I can't even shop alone or be away from my mom (the only person I feel safe around) without having to deal with it. You can usually find me with the deer-in-headlights look because of this, and god forbid someone gets too close to me in the store or walks up behind me stealthily. It's the worst.

I hope you're doing well