Healthcare personnel are continually exposed to occupational stress, burnout, and chronic fatigue arising from the demanding conditions of hospital environments. Although the built environment is increasingly recognized as a determinant of staff mental health, its role in shaping self-efficacy and subjective well-being remains underexplored. This study aimed to identify and validate the spatial dimensions of healthcare-environment design that support these psychological outcomes from an expert perspective. An exploratory sequential mixed-methods design was employed. In the qualitative phase, 17 architecture specialists were selected through purposive and snowball sampling, and data obtained from semi-structured interviews and a review of 211 sources were analyzed using open and axial coding, yielding 58 axial codes. In the quantitative phase, a 38-item questionnaire, developed on the basis of a goal–content matrix, was administered to 29 experts and analyzed using Q-methodology (KMO = 0.697; Bartlett’s test, χ² = 597.523, df = 325, p < 0.001; Cronbach’s α = 0.926). Seven core spatial dimensions were identified—flexibility, spatial organization, naturalness, spatial diversity, vitality, participation, and safety—each associated with reduced occupational stress and enhanced concentration, well-being, and self-efficacy. Findings further revealed that these effects are indirect, operating through perceptual, psychological-restorative, social, and professional pathways, and that experts conceptualize healthcare space through five interrelated systems of thought: dynamic spatiality, ecological orientation, interactive naturalness, responsive controllability, and action-oriented functionalism. The coexistence of these perspectives underscores the need for a multidimensional, multi-pathway approach to evidence-based healthcare-space design