you might better off using fragments of scales and arpeggios with all the 'pungent' notes taken out... the wider the intervals you use, generally the better... you'll never sound peaceful with dense chromatic clusters
basically, intervals like 4ths and 5ths are good.. they don't give your ear much information to chew on
try stacking 5ths... eg a C - G - D... which gives you a nice open sounding add9 without a 3rd tying things down too much
a pentatonic minor figure WITHOUT the 3rd has lots of these ambiguous, 'open' sounding notes too
the only other thing I can think of to say is that music teachers often differentiate between harmony that exists because of chord movement, and harmony that exists due to repetition or reinforcement.... e.g. 'traditional' harmony defines a tonal centre by the presence of cadences/resolution etc... wheras modern music often defines a tonal centre just through the restatement of the same chord over and over
I'd suggest you'll get more mileage in the 'peacefulness' stakes if you go for the secondary approach and have your harmony as static as possible... traditional harmony is obviously based on tension & resolution, which is what you're trying to avoid
