Diabetic foot ulcers (DFUs) are a major cause of lower-limb amputation worldwide and arise from complex interactions between neuropathy, ischemia, and mechanical stress. Current screening protocols are often insufficient to detect early physiological changes, especially in asymptomatic patients. This study proposes a systematic framework for selecting pathophysiological variables suitable for wearable monitoring in DFU prevention. Based on an interdisciplinary review of clinical classifications (IWGDF, SIGN/SCI-DC), risk mechanisms, and technical feasibility, six core variables were identified: plantar pressure, shear/friction force, skin temperature asymmetry, peripheral pulse, tissue hydration, and microvascular perfusion. Clinical reference thresholds for each variable were extracted from the literature and used to validate the suitability of low-power, wearable-compatible sensors. All selected sensing modalities operate within ranges compatible with these thresholds. We present the conceptual design of DIAPODAL, a wearable system aimed at real-time lesion risk detection in early-stage patients. This work provides a structured methodology to guide the development of a preventive tool for diabetic foot care.