Advice for mid section with a slipped disc.

I'm not massively overweight, 47m, 6ft 2 & 89kg's. Only started working out & eating more healthy 4 months ago.

I have a slipped disc, so I'm limited in what excersices I can do safely. I'm happy with the progress in my upper body & legs, but not with my mid section.

Any suggestions on how to get that section looking more atheletic? I do a bit of walking 15m 3 times a week, recumbent bike 5k 3 times a week & i play golf, walking the course once a week.

I'm not looking for diagnosis or medical advice, just any excersices I can consider/test out.