Two functions of a 1-year-old bday: You celebrate with YOUR friends (and their families) that your darling baby is a year old AND you can have some pictures for your child's albums to show him how you celebrated his birthday.
So, since your child won't remember it, do what you want. Big, small, your friends, or just your immediate family. Even if it's just you, your husband, your son, and a little trip to the zoo, that would be cute for the baby book too. You don't have to have a party. But, if you do, that's fine too. Any kind of party you're comfortable with will honor his birthday just fine. Make it as small as you want. Have fun!