Planks can help that area (as well as the core, including the abdominals that support the lower back).
"supermen" or "birddogs" also work.
Superman: lie prone (face-down) on the floor, with arms out straight in front of you. Start by lifting one arm ad opposite leg off floor, going for "length" rather than "height". No crunching of the lower back. Then you can progress to doing both arms, or both legs (or alternating) or both arms and legs at the same time (the full 'Superman" positiion).
Birdogs: get on all-fours position. Lift one arm straight out,and opposite leg. Hold. Do all reps on one side, or alternate sides.
Back extensions over a ball also help.
Lying prone on a stability ball, with the ball under your hips and weight on toes, feet rather wide (at first). Cross your hands, elbows out, and rest your forhead on the hands. Using the strength of your back and glutes, lift your upper body to parallel or a bit higher. Again, no arching in the back, just length and lift.