Room thermometer
Official targets differ: the NHS says 16–20 °C, German paediatricians 16–18 °C, French health insurance 18–20 °C. Use it to choose the sleeping bag’s TOG.
Beurer HM 16 thermo-hygrometer: 16 €
Philips Avent Digital bath and room thermometer SCH480/00: 17 €
TFA Dostmann Comfort Control thermo-hygrometer: 23 €