Affiliate vs Adsense or what?

Guys, We have a site with Travel niche, We working on Travel to Iran options. I am looking for some side earning, anyone have an idea how can I make more money with this site? at the moment we selling tours and travel services.

PR: 4
DA: 27
Facebook, Instagram, Pinterest, Twitter and ....
Monthly Visitor: 20K
Country: US, Iran, Germany, UK

Thanks.