Through the mill is an idiomatic phrase which refers to experiencing a difficult or challenging time. The antonyms for this phrase can be words or phrases that connote feelings of comfort, ease, comfortability, joy, happiness, freedom or convenience. These antonyms may include, for instance, 'smooth sailing,' 'a bed of roses,' 'a walk in the park,' 'a breeze,' 'uneventful,' 'pleasure,' 'luxury,' 'cushy,' among others. These words have the opposite effect of the challenging or difficult experiences that one might face when going through the mill. Therefore, when it comes to the antonyms for the phrase 'through the mill,' it's all about focus on opposite experiences that bring joy and happiness to someone.