I am in much the same situation. I hated to give up heavy weigh lifting and rowing, but decided I would rather live to a ripe old age. In addition to walking, I discovered reformer Pilates, which is as much about breath control as it is about core stabilization. If you find a good studio with nationally certified experienced instructors you will learn how to breathe through planks and squats and avoid the valsava maneuver that spikes your blood pressure. The reformer springs provide some resistance, not as much as heavy weight lifting, but it is effective. I've been doing this for 4 years and had no change in the size of my AAA. I don't know of any research that looks at Pilates, but my cardiologist was fine with it.