Ring of Warmth (3.5e Equipment)
From D&D Wiki
The ring of warmth makes the wearer feel a minimum temperature of what is necessary to feel warm. For example, a human would feel a minimum of 70 degrees Fahrenheit (21 Celsius). This ring has no effect if the wearer is in temperature that is higher than what is considered warm for it. Wearer is immune to hypothermia.
Cost: 5,000 GP