According to Psychology Today, the definition of Mindfulness & Gratitude are as follows......
Mindfulness is a state of active, open attention on the present. When you're mindful, you observe your thoughts and feelings from a distance, without judging them good or bad. Instead of letting your life pass you by, mindfulness means living in the moment and awakening to experience.
Gratitude is an emotion expressing appreciation for what one has—as opposed to, for example, a consumer-driven emphasis on what one wants.
Mixing them together is a wonderful daily occurrence.
For me being mindful of my negative thoughts & letting go of them has been profound. There in lies the gratitude. Always be grateful for your present state of awareness. No self judgments, no regrets. Just asking myself "How does it get better then this?"