Question about a promise ring?

My boyfriend and I have been together almost a year and a half and we couldn't be more in love. We spend every day together, tell each other everything, and always have the best times together. A few girls I know have gotten promise rings from their boyfriends, and I feel silly because I REALLY want one (for the right reasons obviously, not just because you think I'm falling into the "everyone's getting them" bandwagon) but clearly I'm not gonna say, "Hey I want a promise ring." I honestly don't know if my boyfriend would think of something like that by himself haha but what are some indirect, really discreet ways of suggesting something like that? Thank you!! :)