Save your gold money, and use it to buy African Kingdoms instead!

Since you're playing The Forgotten, we can safely assume you're running HD version. This means that for mods, you only need to look as far as the Steam workshop.

Get there from the AOE2 page on your games library. You can either browse or search. For an example: One mod I strongly recommend as a player returning after a long time is the custom AI made by Twitch personality Resonance22, which is helpful because it'll give you tutorials while it kicks your ass. Find it with the search bar, and then click the subscribe button. The mod will download when you launch AOE2HD.

They'll load. You'll see this screen while they do. Then you can use them as described in the mod's page.

Some mods, like the infinite population mod, require you to actually tamper with the data files. PM me if you need a walkthrough on those.