I often tell my students that many yoga poses require a strong core. Without it, don't even attempt some of the more advanced poses like a headstand or side crow.
Boat pose, aka navasana, is an excellent core-building pose that most everyone can do with modifications. If your abs and low back muscles don't allow you to have your legs and torso in a nice V shape, try bending the knees, or placing the hands under the thighs. In the traditional pose, hands reach forward as you balance on the coccyx bone.
As mentioned in my book, "From the Boxing Ring to the Ashram: Wisdom for Mind, Body and Spirit," I began yoga when I was just a teen. Suffering from severe low back pains, an orthopedic surgeon recommended simple back exercises and core strengtheners to reduce the pain. My book features a medical practitioner that I consider to be the leading guru for yoga and the back. Dr. Loren Fishman describes how and why a strong core can relieve your nagging back (depending on the diagnosis, of course). In particular, he suggests the boat pose for people with spondylolisthesis. Often caused by a sports injury, spondylolisthesis occurs when one vertebra slides (usually forward) on the one beneath it. Stretching and strengthening the low back is often beneficial.