Subglacial bed topography is a fundamental boundary condition for ice-sheet flow, basal thermal regimes, and the preservation of palaeoclimate records, yet it remains highly uncertain across Antarctica. We use stochastic simulation methods to generate an ensemble of gridded (500 m) ice thickness and bed elevation near Dome C, and map bed elevation uncertainty accounting for impacts of data availability and basal roughness. New airborne radar measurements uncover previously undocumented sectors of the ice-bed interface and we integrate these with existing data using a rigorous approach to ensure nearby measurement compatibility. Our simulated bed shows improved representation of basal roughness between survey profiles, revealing regional roughness over 50 % higher than previous interpolations. We apply the ensemble to investigate uncertainty in meltwater routing, identifying well-constrained drainage away from the Dome C Plateau but poorly constrained outflow from Concordia Lake and parts of the Belgica Highlands. Topographic focussing of geothermal heat predicts local anomalies up to ±30 % relative to the regional value, and several ice core drill sites are in a zone of 12 % locally-reduced geothermal heating which is favourable for deep ice layer preservation. This work demonstrates that the critical subglacial bed boundary condition is better represented by ensemble-based, stochastic simulations based on strictly cross-validated data rather than single deterministic interpolations, and simulated beds can improve the reliability of analyses with robust consideration of uncertainties in data-sparse regions.