Every October, my phone starts lighting up with the same text from clients: “The furnace kicked on last night and I think I slept in a sauna.” Here is the cruel math of heating season — the same night your partner finally stops complaining about cold feet, your internal thermostat decides that 2:47 a.m. is the perfect time to open every oven door in your body at once. You kick the duvet. You flip the pillow. You lie there doing arithmetic about how many hours remain before the alarm while your sleep tracker quietly records a disaster. I coach women…