An optimized, multi-configuration cabin and lavatory arrangement for a single aisle aircraft that adds either another row of seating or increases cabin space without sacrificing performance or function of the existing components. The invention includes a space efficient lavatory that may incorporate various design configurations to meet the needs of airlines seeking to generate additional revenue. The configuration of the present invention uses a reduction in the lavatory floor plan with the option for a modular flex wall area to provide a customizable combination that gains extra cabin space for carriers that can be utilized for additional revenue streams.