I'm not a fan of chiropractors either but people here seem to really like McCormick. I read his older book years ago. I think I read them all at that time and it's good to get a broad perspective.
Sounds like you're doing quite a lot of exercise that might be helpful. Tai Chi is really good for balance and if it's fun, that's a bonus! Also, when we do those slow, targeted movements I think you get this mirco tweaking of your muscles that we don't get with the larger movements.

The core exercises I do are mostly bicycle reps and toe dips. Since I do them in bed, my back is flat and fully supported by the mattress. I don't crunch or curve my back though I do lift my head and use my arms. I don't know if that's contraindicated for some as it does involve lifting at the cervical spine though you can do the exercise without lifting your head.
For the toe dips, those are completely safe. Back is flat, legs up in a table top position at a right angle. The first sets I do are dipping both toes down to the mattress (not touching it) and then returning to start position. After that set, I then dip one toe down, return to table top and alternate. (then I do a bunch of other stuff)I learned this exercise from a PT who I went to when I was having back discomfort. When he introduced this exercise, I couldn't do a single one of them though I thought I was strong! Didn't take too long before I had the strength to do hundreds.
The back lifts are laying flat on the stomach, arms bent in right angles aligned with the shoulder. Lift up using your back muscles and pulse your arms in that lifted position for 50 counts. Then lie back down and in that same position, lift and lower you upper body for 50 counts. I am told this exercise is safe for osteo but best not to go to end range and crunch the back. Strengthening the back muscles and core is great for strength, stability and balance and let's hope, for a little gain in bone density too! That's a long shot but worth the effort.