First a definition - the correct definition of a mitzvah is "a commandment." It is more than a good deed - it is something humans are obligated to do in order to enhance their relationship with The Divine. (The plural form of mitzvah is mitzvot, i.e. commandments.)
Over the centuries, Jewish rabbis defined 613 mitzvot. Do I think you have to follow these commandments to be a good person? Of course not.
Do I think these mitzvot are the only way to create a meaningful relationship with The Divine? No. I think more than one wisdom tradition has created a convenant with God. The Jewish tradition speaks to me and is my preferred way of connecting with my higher self and the Essence of the Universe.
That doesn't mean I follow every commandment in the Bible or written by ancient rabbis. I'm exploring a path that is meaningful to me. There's no law requiring Jews to wear a head covering, but it helps me to feel closer to The Divine and my higher self, so I choose to wear a yarmulke. On the other hand, I'm not sure kosher dietary practices change my relationship with The Divine, so I eat kosher style. I don't mix milk and meat, don't eat pork or shellfish. But my kitchen is not kosher and the meat I buy isn't kosher. My parents will tell you this "kosher style" thing doesn't exist. Then again, they don't bother with any dietary restrictions. More to come..