I haven’t yet started treatment specifically for my BPD, but I know what treatments haven’t worked for me in the past when my issues were perceived as only anxiety and depression. I found that typical CBT and ACT weren’t very useful to me, as the therapies (or the ways they were delivered, I guess) just didn’t seem to address my problems or be based on an understanding of what I was actually experiencing. I was lucky enough to eventually find a psychologist who encouraged me to share what hasn’t worked for me in the past and to discuss with her what is/isn’t working in our sessions, and she tailors her approach based on that. From memory, I think her approach has included aspects of DBT, Schema, Narrative, and a little CBT (but I could be misremembering some of those!), and I have found this to be the most helpful approach for me.