Some of the books on happiness I love are:
The How and Why of Happiness by Sonja Lyubomirsky which gives a really easy read on the research. It shows how powerful those small daily choices are
The Happiness Project by Gretchen Rubin which outlines a year in her life where she tried all sorts of strategies to be happy
And the classic (although not the easiest read) is Authentic Happiness by Martin Seligman
One of the best things I got from The Happiness Project sounds so incredibly trivial but has become pretty important to me. She talks about the importance of being physically comfortable. Making sure you are warm enough, have comfy clothes, the things you need. It made me realise how often I used to sit around with freezing feet, wishing I had bothered to change out of my work clothes.
Now I take the time and, strangely enough, I really am happier in my uggs and sweats with the heating and lighting on just right.
It really can be the small things!
