promise ring

Ive been dating my boyfriend for a couple years. We're both not quite ready for marriage but our relationship is very special and we have plans of being married. Recently he asked me what I want for christmas. I don't really want anything, except a promise ring came to mind. Not sure how to ask him or bring it up. And not sure what his reaction would be. Thoughts? I am in my early 20s and he just entered his 30s so this isn't a high school love situation.