Spin supersolids emerge as a central topic in frustrated magnetism, motivating the search for realization in quantum materials. To this end, we study the origin of exchange anisotropy, Δ, in triangular-lattice cobaltate families X₂YCo(PO₄)₂ and X₂Co(SeO₃)₂ (X = Na, K, Rb, Cs; Y = Mg, Ca, Sr, Ba) by tailoring realistic spin models. We show that Δ is determined by the ratio of trigonal crystal field to spin-orbit coupling strength. This framework explains contrasting anisotropies in these families, predicts systematic trends in Δ across X/Y-substitutions, and identifies candidate materials for spin supersolids. Our results establish trigonal field engineering as a microscopic route toward the design of spin supersolids.