The person you are marrying is a match for you in more ways than one, so why not let it be the same with the rings the both of you wear. A matching and massive diamond ring pair declare no uncertain terms that you value being with each other and prefer it as a lifelong option. There are, however, some things to watch when picking out matching rings.
Yellow gold is well and good, but it simply does not suit some people. Consider white gold or platinum gold if that is the case with you and your spouse, and maybe the option of alloying differently shaded metals.
Modern rings generally have enormous gems on them, or at least stones of sizes the owners can afford. Diamond-set rings are not the only option to look into, because there are plenty of other gems that bring a stunning look.
This is a good way to bring in subtle personalization using your own individual flair. Mull over the options of engraving words, phrases, designs, etc., on either or both sides of them, and pick the one you and your fiancée really want to go with.