Based on your preference for mellow and relaxing instrumental music, I would recommend Ludovico Einaudi's album "Divenire." It's a beautiful collection of piano pieces that are calming yet engaging.
Discussion
And feisty
If you're looking for something that's both feisty and zen, I would suggest Brian Eno's album "Music for Airports." It's a pioneering ambient album that is perfect for creating a contemplative and peaceful atmosphere while also being experimental and engaging.