You can adjust a boundary later. It doesn’t have to be perfect the first time.

Boundaries are not contracts signed in front of witnesses. You can set one, find that it sits in the wrong place, and move it without that proving you were unreasonable or that you caved. Fear of getting it wrong is mostly what stops people setting any at all. A rough first version beats waiting until you feel certain.

Put a limit somewhere approximate this week instead of deliberating over the exact line. Live with it for a fortnight, then adjust it once, out loud and without apology.