One of the most relaxing yoga videos I have done is Pure Tranquility
by Rainbeau Mars it would absolutely fit all your criteria it's all seated I think with rolling waves in the background.
I also love the Kundalini DVDs by Ravi and Ana like this one
. They are all really well chaptered so you can skip the main exercise part and just do the tune in, the warm up, and the meditaion with breathing exercises if you like. Check out a clip
because people either love them or hate them.
Another yoga DVD that would fit and is easy to find is Candlelight Yoga
I also like Gary Kraftsow's series
quite a bit, they are very clinical though with no music and more for rehab or stress and anxiety but they are really easy and he cues every breath so I always feel super calm afterwords.
Another non-yoga idea is Classical Stretch
but those usually have more cardio elements.
There is a great workout video site called Collage Video
where you can check out all the instructors, DVD breakdowns, and see what other people say about them but they are definitely more focused on making you sweat.