i suggest you to book direct via the airlines website, you can certainly use cheapoair and google flights to see the flight deals but try to avoid booking from third party websites as you may have to face a lot of hassle if you have to change flights or even cancel it. It is better to be safe than sorry you know!

kayak or google flights. They give option to buy directly from them or airlines or third party (like vayama). Last Dashai I bought the cheapest fare from vayama (Turkish Airlines, $1200 round trip that included a free overnight hotel, dinner and breakfast), which I found from Kayak.