We most certainly can think our way out of sadness and depression, although I would never presume to advise a bereaved parent. That is so far out of my experience and out of the natural order of things. I am sorry for your loss.
Mindfulness is a very powerful cognitive tool, it was helpful to me in dealing with my depression and anxiety. I still use it often. It is like a mental vacation, and it is always available to me whenever I need it.