I don't think it is necessary to buy a map. There are many road signs in the Forbidden City. You can find your way. My friend is a road idiot, and he didn't get lost in it, haha.
The Forbidden City is very big. If you are an old man, look at the three halls and the imperial garden, and the Jubao Hall is similar. Among them, Jubaotang is a must! Those who have physical strength can go to the West Sixth Palace to have a look. There are articles for daily use used by Zinuo in those years, which are of great appreciation value.
If it is a one-day tour, it is best for the elderly to bring some food and water, and umbrellas are also necessary. If the weather is hot, pay attention to heatstroke prevention and cooling.