Realme, I think you've made such an important point about looking for comfort, not pain. A lot of people SI because it gives them a reason to self care afterwards, such as cleaning the wound, bandaging etc. it's the only way they allow themselves to get comfort.
Can you find any other ways that might make you feel comforted, and try these when you get the urge to scratch and bite? Maybe a warm bath, or give yourself a hand massage with scented oils. It may provide a little bit of the comfort that you need.