This! A thousand times this!
You can start small. Sit on a chair and slowly bend down, at the waist, keeping your back arched the whole time. Go as far down as you can (until your upper body is about parallel to the floor), and then sit back up, still keeping your back arched.
This targets the muscles of the lower back, and is called a good morning. You can do them standing, too, and as you get stronger you can progress to adding weight across your shoulders.
Strengthening those muscles will go very far in reducing pain.
Also very true! Exercising the entire midsection is important for reducing back pain.
Don’t be afraid to use weighted resistance when doing abdominal exercises, either. They are muscles, just like biceps or pecs, and so they benefit from the progressive overload of increasing resistance.
And this touches on the larger point, which is that the muscles of the body work in cohesion. So a truly comprehensive exercise plan to address back pain should actually exercise the entire body.
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Another musculoskeletal issue that can lead to back pain is tightness. Try stretching out the hamstrings and glutes to help alleviate some back pain.