The Gemara (Nedarim 20b) establishes the foundational ruling directly: the law does not follow Yochanan ben Dahavai, and instead a man may do with his wife whatever he desires.
The Mishneh Torah, Issurei Biah 21:9 codifies this by specifying that a husband may kiss any organ he desires, provided he does not release seed in vain — language that straightforwardly permits oral contact.
The Shulchan Arukh, Even HaEzer 25:2 affirms the same permissive rule — kissing any limb, vaginal or anal intercourse, or intimacy without relations — while adding that even what is permitted calls for personal sanctity, and one should not pursue marital relations primarily for pleasure but with proper intention.
The Arukh HaShulchan, Even HaEzer 25:8–9 adds the important qualification that consent governs the entire domain: a husband may not coerce his wife, as acting without her knowledge or agreement is itself a violation.