In this manuscript, a highly sensitive Bloch surface wave (BSW)-based sensor is proposed for refractive index sensing analysis. The structure is designed using an one-dimensional photonic crystal (1D-PhC) structure. A top defective layer of transition metal dichalcogenides (TMDC) material with atomic layer thickness is introduced to confine a Bloch mode analogues to surface plasmon-like mode at the top interface. The detailed analysis is carried out to investigate the impact of number of TMDC monolayers on sensing performance. The wavelength (angular) interrogation provides the significant higher sensitivity of around 9650 nm/RIU (or 231°/RIU). Besides the sensitivity, the rigorous analysis of full-width-half-maximum (FWHM) and figure-of-merit (FOM) is also carried out and a FOM of around 48,250/RIU (38,500/RIU) has been reported. The proposed design possesses the advantage in terms of easy fabrication and integration capability to develop handheld senor systems, especially for biological and chemical sensing.