Glad this was helpful. The exercise ball is good because you can allow the ball to both support and start very gently. Try to get the damaged disk area near the apex of the ball so you get maximum support. Also, no soft ball! Make sure the ball is pretty firm and if is squishy, it really doesn't help. I would suggest not trying to do a full crunches but rather start with concentrating on tensing your stomach muscles and holding for, say 5, seconds. Do a few sets of 10. Then move to 10 seconds holds. Then start with small crunches that are small. Then turn over and start with very small movements here as well. Don't go crazy, you do want to put a great deal of force on the back to start and allow the ball to give you support. This will give your back tremendous help and support so be patient to get there. If it takes a month, that's fine. But I think you will start seeing results even with the small steps.
Yes, the gluts are super important and so overlooked. Why do so many middle aged and older men have no butts? They have allowed their gluts to atrophy and they leave themselves open to back problems.
Also, it is hard to describe but the pillow is very important as well. No matter how good your mattress is, it doesn't give enough support for a damaged disk. This will allow you to create a cradle for your back and to work it down to where it is perfect. Millions of tiny beads all creating the perfect support. Now a word on how they come. It may feel that it is too firm. I would suggest sitting on it around the house to stretch the cover. If you don't get the result you want, you can create a tiny slit in the seam and get rid of some of the beads. Eventually it will stretch to where you probably need to get a new one in a few years. There are several companies that make them, but you want to cover to have a great deal of stretch. https://www.amazon.com/Mooshi-Squish-Microbead-Jelly-Pillow/dp/B01CCKVXG0/ref=asc_df_B01CCKVXG0/
Yes, if I had known what I know today, I would have had the rods removed in a few years after the support was no longer needed. But, they have fused into my vertebrae and no surgeon wants to touch it. But I actually have pretty good flexibility above it so I don't have any limitations much. But yes, the L4 disk issue was most likely caused because of the stress placed on it from the fusion above. I truly am blessed on what I can do. I ran long distance for years and even a marathon. I'm into shorter sprints now but am still pretty fast. My University friends are all on their hip and knee replacements but I prefer to invest the work at the gym. Oh well, it is time to head off to the gym!