Finding a good therapist is good idea at first, then to transition to an educated personal trainer who is familiar in fascial connections, mobility and activation. I work with people in your position who are in between therapy and training quite often. Don't neglect the bundled up scar tissue and fascia which needs to be rolled out first, then stretched, then strengthened through activation using local, not global, total body/core exercises. As the above people said a DNS therapist and yoga is great also, as it targets these fascial meridian "cobwebs" connecting one part of the body to the other.
Since your superficial front line is obviously tight, and pulling the front of your body, I would stretch that first with yoga stretches after some myofascial release using any ball maneuvered around the border of rib cage. Throw in hip flexor stretches as well since you ride the MTB often. Then strengthening the superficial back line with some glute bridges, quadruped opposite arm leg raises or something similar.
If you want to do things on your own and rehab yourself, I suggest reading Anatomy Trains by Thomas Myers and How To Become A Supple Leopard by Kelly Starrett. Great knowledge for anybody to have if you're into healthy aging. Good luck!
