You're doing it right.

Moving walkways were designed to help people walk faster across large spaces like airport terminals, not excuse them from the minimal exercise of walking. But they do also serve people who actually can't walk great distances.

I'm one of those people who always walks on the moving walkway, and I get frustrated when inconsiderate people sprawl across the entire width, blocking my way. I'll call out to pass. Sometimes I'm a little brusque about it. I am extra patient, though, whenever I spot someone with a mobility device such as a cane, crutch, or walker. I understand (partly from first-hand experience) that such people may not be able to step to the side so easily. I appreciate that you are making every effort you can in advance.