For your requirements, a GeForce GT 610 is what you are looking for.
More than capable of 1080p blu-ray playback, and drawing a maximum of 29W.
Actual power draw in typical use is likely lower.
The GeForce GT 620/630/640 all meet your requirements as well.
The maximum power draw on these cards is higher, but actual power draw while watching a movie is probably very similar.