Split adjustable mattress foundation for multiple users

Adjustable mattress assemblies and processes including an adjustable mattress foundation dimensioned to support a mattress configured to accommodate two supine users during use thereof includes a foundation frame including a first sub-foundation configured with at least one motorized actuator to effect inclination or declination of the mattress support surface and an abutting second sub-foundation free of a motorized actuator. The second foundation is mechanically coupled to the first foundation such that articulation of the first sub-foundation results in a similar articulation in the second foundation. The first and second foundations have similar length, height and width dimensions, which collectively approximates the size of the oversized mattress configured to accommodate two supine users, e.g., king size, queen size, California king size, or the like.