The Thailand forum on FT, of course, which is probably where this thread should be.

IIRC, Floor 3 does not have moving sidewalks. But you can stay down on Floor 2, the arrivals floor, and use the sidewalks on that floor to get you at least halfway to the opposite side of the airport, since the sidewalks on that floor all operate toward the center of the D concourse. After reaching the center, keep walking (now against the flow, but the concourse should be wide enough) until you reach the transfer point for the B and C concourses. You will have to pass through one duty-free shop on Level 2, perhaps two shops, but that's it. Very few shops on Level 3, mostly lounges.