“Let me think about it” is a complete answer. You don’t owe anyone an instant yes.

Not every question deserves an answer in the moment. The pressure to reply immediately comes from the awkwardness of the pause, not from the decision, and choices made to end a silence are the ones people most often regret. Asking for time is a real answer, and it tells the other person you are treating it seriously.

Use it on the next thing you feel rushed into: a shift swap, a plan, a favor. Say when you will come back with an answer, then come back. Anybody who refuses to let you think has told you something about the offer.