Every injured spine is unique; other people's experiences may give you ideas, but your results will be based on your particular situation. Take advice as data points and nothing more.

Having increased flexibility will almost certainly help. The question is, can you increase your flexibility without causing injury? Not everybody can.

Ditto with increased core strength.

(I improved both the above by taking up the unicycle at age 54)

A pro fit, by a fitter who is familiar with riders having physical challenges, will almost certainly help. Beware fitters who don't have any such competence.

It's quite possible this will take time and a combination of changes. Patience and persistence will pay off.

(Lower back issues and neck arthritis eventually led me to a recumbent for rides over 20 miles. I've ridden my upright bike on a couple 200k brevets, but finished in great discomfort. On the bent I've completed 24 hour races and a 1500k brevet, finishing fatigued but without significant pain. Again, just one data point, and not necessarily pertinent to your condition.)