It is not only good deeds that bring about happiness; deeds are only a factor. This is indicated by Allah's saying,
...enter you Paradise, because of that (the good) which you used to do (in the world).
As for the Prophet's (peace be upon him) saying,
No one of you will enter Paradise by virtue of his deeds,
it means that Jannah cannot be the corresponding reward for one's good deeds. In other words, deeds, however great they may be, are not enough a price for entering Jannah. Rather, doing good deeds should be accompanied by Allah's forgiveness and mercy in order to qualify for entering Jannah. Allah obliterates all sins by His Forgiveness, grants all that is good by His Mercy, and doubles the reward by His Grace.May Allah grant us success. May peace and blessings be upon our Prophet
Muhammad, his family, and Companions!