Sharing a 10 year journey here that involved both CBT and ACT. This may be oversimplifying it but I see various philosophies in order of how low they strike at the root. Obviously the implicit advice I'm giving is to go as low to the root (bottom of the list) as resonates with you:

* CBT: challenge negative ways of thinking

* ACT: be aware of thinking (don't overthink thinking), and commit to a direction.

* Mainstream Zen: very similar to ACT without the purpose/commitment component. After all, what's the purpose of purpose?

* Vipassana: super involved with awareness of present starting with a breathe practice. (Mindfulness bootcamp if you can't seem to inquire.)

* Morita Therapy: same as ACT but with a step toward questioning the thinker

* Advaita Vedanta (or I've heard Dzogchen Zen): challenge the thinker/contemplator/meditator. "Who am I?" root out the original thought of a separate self. Recommended: Ramana Maharshi, Papaji, Nisargadatta Maharaj, Mooji (or Cloud of Unknowing if your Christian).