My therapist had me start with very easy variations of dead bug and build up. I don’t remember the exact progression, but it went something like this:
Arms at sides; pelvic tilt, hold
Arms at sides; knees bent, alternating slide feet on floor
Arms at sides; alternating heel lifts
Arms at sides; alternating leg extension
Arms at sides; alternating leg lifts
Once a level started to get easy, I’d add opposite arm moving with opposite leg.
Before I could move on to the next level, he’d put a towel under my back. If my lower back lifted, and he could pull the towel, I wasn’t ready for the next level. My therapist also put a blood pressure cuff slightly inflated under my back and force me to maintain constant pressure.
Once I was able to do strict sit-ups again, I feel like they’ve been an important part of keeping my core strong. Kayaker never feel right, so I’ve been finding other rotational exercises that don’t require rotation under load.
Good luck in your recovery!