Planks, planks and more planks! I am a big fan of the holds as a base core builder. Regular, side planks, shoulder bridges,etc. My physio always recommends working for 10 reps of a 10 sec hold; a bit of trembling is ok, but as soon as you lose your form or start to actually wobble, stop. You want to be solid for the full hold.
If you have the time, find yourself a personal pilates instructor (mass classes are probably not as helpful since you are working with a specific condition). Make sure they have training in one of the big names, like Stott. A ‘fitness pilates’ trainer won’t have the background to help you properly. Once you have the basics, you will find it very helpful to be able to apply the core stabilization principles to everything you do.
Best of luck!