Joint bank account. Combined phone plans. Joint insurance policy. All showing your place of residence same as him.
Would add, any bills or purchases in one or both of your names - as long as not just from one of you. Any correspondence or bills, deliveries, payments for furniture purchased, etc.
You can also get letters from friends/family or lease agreement from parents.
Note: since you have been together for several years, document that as well. if that long-term relationship is well documented, the question of how much proof needed of living together after being married will likely be much less important.
[Or to put this simply: a couple that has only known each other for a month before legal marriage
obviously will need more proof of living together after marriage to be credible. A couple that documents well their five-year + relationship living together and has kids probably doesn't need much at all. (Those in between, like you, well, in between those two cases)]
Warning (for others reading this): proof of living together for common law spouses is a different matter with its own nuances and critical points - eg a couple can be married without ever having lived together, but not common law.