The disclosure generally relates to an adjustable bed apparatus, in particular an adjustable bed foundation. The adjustable foundation can include a rail system such as a detachable rail system, which can be configured to conceal mechanical and support substructure beneath the mattress support surface of the adjustable bed. In some embodiments, the rail system includes a mounting element and a corresponding rail or board mounted to the adjustable foundation, such as to the subframe of the adjustable foundation. The adjustable foundation can include independently adjustable lumbar and neck support structures on an adjustable back/head section of the adjustable bed foundation. In some embodiments, the lumbar and neck support structures include inflatable air bladder structures. In other embodiments, the lumbar and neck support structures include mechanically actuatable subsections of the adjustable back/head section of the adjustable bed foundation