Minimalist approach:
Calcium Chloride and gypsum to attain about 50 ppm Ca, 80 ppm Cl, 30 ppm SO4. Baking soda to get mash pH around 5.5, ending with Na as low as practical, under 25 ppm if possible but definitely under 50 ppm.
There's wiggle room with all those numbers; this is hardly a prescriptive approach, just a ballpark.