Suction hammock — a spot in the sun, no furniture

The answer when there is no ledge, no radiator, and no room for furniture. Four suction cups on the glass, washable cover, mesh seat that lets the sun's warmth through. The cat sees outside, which is half the point. Suction cups hold on clean dry glass, not on dusty double glazing or on a frame. Re-seat them every fortnight, and stay under seven kilos.