I just wanted to say one thing regarding finding a good T for you: lots of Ts probably don't put "I work with self harm" or something like that, mine certainly doesn't. That's because it's mainly considered a symptom and a "bad" coping skill. The symptom part is important because at least here, they don't usually list symptoms, they list specific illnesses, like depression, BPD, DID... somebody with BPD might or might not struggle with self harm, listing every possible symptom would be a bit much. It's easier and more inclusive to say what diagnosis you work with. The "bad" coping skill is important because I've found that at least my T doesn't want to ruminate too much on those. We might have had two full sessions in total that really discuss self harm. The rest of the time, the discussion is something like me saying it's happened again, him asking very quickly to see it, and then he asks why it happened, what was going on, and we might discuss what I could have done differently. I think he does it like this because concentrating too much on the maladaptive part doesn't make it go away and doesn't give you any new resources. It's like if you were to talk about some trauma over and over while only concentrating on what has happened. It might help short term, but it doesn't really change anything.

Maybe some things you could search for apart from self harm and your own diagnosis is something like BPD or DBT? Therapists who treat BPD tend to know about self harm and they have a bunch of knowledge on how to cope/calm down. Even if you don't have BPD, if they list your issues as well as that, I think that might be beneficial for you.