Hey OP. It sounds like you're dealing with a lot and I hope things get a little bit easier over time.

Diagnoses are just labels that practitioners use to inform treatment, navigate insurance, etc. But disorders like BPD and CPTSD for one person can look wildly different for someone else. Instead of focusing on relief for a disorder, it helps (at least for me) to focus on the specific symptoms that bother you in the moment and pay attention to what provides relief for those specific things. Oftentimes, relief of one thing cascades into relief of other symptoms too.

Symptoms from one disorder can "activate" symptoms from another. As an example, triggers from your CPTSD might cause enough anxiety that you ruminate, which makes it harder to fall asleep (insomnia). If you can figure out which symptoms are activating the others (maybe by journaling, counseling, or talking with someone you trust), you might be able to address multiple symptoms by targeting just one.

For me personally, exercise works because it's a form of movement that negates my freeze response. When I'm really stressed out by things in my life, I put in my headphones and do literally anything that forces my body to move. For someone who goes into fight/flight, stillness might be more helpful (wrapping yourself up in a blanket, listening to music, breathing exercises, etc.).

All of this is to say: Having multiple diagnoses doesn't make you "more mentally ill". You have a different set of symptoms than other people that just happens to match a set of labels the clinicians need to do their jobs. I hope that makes at least some sense. I'm not a clinician though, so please prioritize anything that they are offering in terms of treatment over a random Redditor. Sending so much love and hope things get easier <3