How do I write session notes without them taking over?

You can write a note now; the trouble is that a session note can eat you alive if you let it, chasing every nuance until an hour disappears. The care that makes you a good clinician is the same care that makes the note bottomless. That is worth naming. A note does not have to hold the whole session. It has to hold what matters clinically, enough to be accurate and useful and to protect you and the client. The rest of the richness lives in you and in the room, not on the page. Let the page do less. Give yourself a time limit and a simple structure, a few headings you fill each time, so the note has edges. When the time is up, it is done. Trusting a lean, honest note frees you from the endless one, and gives you back the time the work actually needs.