I need a weekend away, so _______________________________ something on the Internet.

The selected answer effectively conveys the speaker's intention and the action they took in a conversational and informal manner. It emphasizes the decision made regarding the weekend getaway, providing a personal touch to the statement. By stating "What I did was book," the speaker clearly informs the listener that the action of booking was the key focus, which aligns perfectly with the need expressed at the beginning of the sentence.

This structure also suggests a smoother, more natural flow of thought, allowing the listener to quickly grasp the speaker’s action in response to their desire for a weekend away. The phrasing makes it clear that booking has already taken place, fulfilling the original intent stated in the prompt. The other choices, while potentially relevant actions, do not align with the context of expressing the desire to organize a trip.