The floating buoys are an emerging source for renewable energy harvesting using ocean waves. Various point absorbers have been developed based on multi-freedom oscillating structures to capture wave energy. However, the choice of geometrical parameters for buoy design is still a critical problem. This paper presents a novel method to develop new geometries of floating buoy for wave energy harvester (WEH) in heave motion and aims to maximize WEH absorbed power and performance. Fives shapes (Cyl-Cone, Cyl-HS, Cyl-TCC, Cyl-AS and Cyl-SP) were derived from a cylinder buoy based on identical parameters (radius, draft, mass, water-plane area, volume and natural frequency). The Cyl-HS buoy was selected as a reference buoy for comparative analysis. The effects of shape change on the performance and output power were investigated for regular and irregular wave conditions in ANSYS AQWA at an incident wave frequency of 0.22 Hz (low energy density seas). The optimal resonant buoy was identified employing optimal and sub-optimal modes of the PTO system at external stiffness and damping parameters. Moreover, the performance of resonant buoys in optimal and suboptimal working modes was validated statistically using the F-test for variances of two samples in Origin Pro (2019). The energy conversion efficiencies of Cyl-AS buoy were examined as highest among others, with a maximum of 8.4% and 7.4% rise in optimal and suboptimal PTO modes for regular waves, respectively. For irregular waves, the Cyl-AS buoy resulted in maximum output power of 33.9% higher than the Cyl-HS buoy (reference buoy) with a maximum conversion efficiency of 90%. Finally, the simulation and experimental results for the scaled model were compared for RAO and average power and found a good agreement. The findings of this research agree with the UN-2030 Agenda for Sustainable Development Goals (in particular, SDG-7 and SDG-14 goals) while providing a path towards clean energy and blue economy developments.