Give the “Dead Bug” core exercise a try! It may have a funny name, but you’ll quickly see why it’s called this and how effective of a core exercise it is. It is beneficial for people with lower back issues and can correct posture problems while you tighten your abdominal muscles.
Lie on your back with your arms extended above your shoulders/head. Bend your hips and knees to a 90 degree angle. Tighten abs and press lower back into floor. Take a deep breath in and as you exhale, slowly extend left leg toward the floor and right arm overhead. Keep abs tight, don’t arch your back! Slowly return arm and leg to starting position. Repeat with opposite arm and leg and continue alternating.