Hmm... Small Happinesses (which is the answer to your question) sounds awkward. Happiness is an abstract noun so it is difficult to visualise more than one happiness I'm not sure exactly what you are aiming for but how about something like: "Little moments of joy" "small pleasures" "brief intervals of happiness"

"small happiness" isn't really a term that English speakers use. If you mean small things that make you happy, a better phrase to use would be "little joys", which is plural.