Does this extra-plush pillow top work on an adjustable base or without a box spring?

Yes. It is rated compatible with an adjustable bed base, and because the deep 5-inch comfort layer sits on flexible pocketed coils rather than a rigid core, it bends smoothly with the base for zero-gravity and head-up positions. No box spring is needed. It also suits a solid platform or slats spaced under 3 inches. Skip a worn box spring, which can dent the soft top unevenly and may affect the 10-year warranty.