Gimbals don't eliminate up down walking movement (and sometimes they can make it worse). Try on a selfie stick, like the El Grande, with the stick pointed forward and horizontal with the camera tilted up. I mention the El Grande because if you hold the stick in the middle, not the back handle, the back end works as a counter balance and can help keep the image flat and balanced, even when walking. You'll also want to practice what is referred to as the "ninja" walk with you knees bent and feet sliding forward.
