I am really passionate about riding and yoga! Have you done any yoga yet? I do a lot of yoga, and I find that the following are great for your back (that's a problem area for me):
Actually, instead of sending you a bunch of different links...Here's one place that has lots of poses and explanations that I go to from time to time: Yoga Poses | Basic to Advanced Yoga Poses | Asanas
My chiro suggested this series of yoga poses, from a company called brushymountain publishing.com. They have yoga series for many sports, but my recommended one was for paddlers. Its two sets of 22 minute yoga in a downloadable format, and inexpensive. I do them both when I have time, or just one a day. Either day, its really helped my core, flexibility, and strength. What I liked about this particular series is they hold the stretches for some time. I am not a fan of flow yoga - flow is too short to gain flexibility.
I will say one thing about all yoga tapes. I wish they (and pilates too) would teach you to use your spine from a neutral position ie no arch and not a flat back. Ok 2 things. I would never do a double leg lift as an exercise, its not a strength building exercise its a test for your back/hip flexor strength. Whenever I heard someone say put your back flattened on the mat, I cringe. We taught that in aerobic classes 25 years ago and now my back is funny shaped - but I digress.
Anyway, just some thoughts. I like the yoga for paddling series. I tried the climbing one, as I used to rock climb, but found it too hard!
My trainer does yoga and says its helped her riding so so so much and helpingher sleep better and feeling more relaxed after long stressful days! She loves it! I might start getting into it!