Caveat I'm not a doctor, but I am a psychotherapist with inpatient psych experience. In my experience, bipolar disorder is treated primarily with mood stabilizer medications, including lithium, depakote, or lamictal, with psychotherapy as an optional adjunct treatment mostly for people who are having difficulty coping with the social, emotional, or physical impacts of bipolar symptoms or medication side effects.
Lithium seems, on average, to be the best tolerated of the 3 meds I mentioned. Why do you think you need a higher dose if you feel like you're doing well? The goal (under supervision of a physician) should absolutely be to be on the lowest dose possible to maintain stability.
Also, I'd be remiss if I didn't mention that bipolar is what may be called a diagnosis du jour, in that it's a label being given to many people who don't actually have it, but instead have difficulty with emotional regulation related to other issues, such as trauma or borderline personality disorder, which are better served by psychotherapy. There are people who absolutely have depressive and/or manic episodes in the context of bipolar disorder for whom mood stabilizers are realistically the only option, though (besides ECT or TMS).
You mentioned PTSD...is that what you'd want to prioritize treatment for? If so, I genuinely would not bother seeking a therapist for bipolar, but focus on finding someone certified in an evidence-based trauma treatment. For this, cognitive processing therapy (CPT) is the gold standard, and EMDR is also an option.
Navigating this system is tough! Good luck, and sorry for the wall of text.