BedJet

The BedJet 3 takes the air route to bed climate: a unit under the bed pushes heated or cooled air directly into the sheets, with biorhythm scheduling and app control. No water lines, no cover to fit, no plumbing a mattress — and instant heat, which water systems can't do.

At $498 it's the cheapest serious entry into the category, and the instant-warmth party trick makes it a favorite of cold sleepers specifically. The trade against water systems is sustained deep-cool capacity; the win is price, simplicity, and speed. A very rational first move before four-figure bed climate.