There were even two apps, Mittäkuuluu by coderus, and Whatsup from older Symbian and Meego times. Both worked fine and were lovely to use, untill the company Whatsapp sent threatening letters from their lawyers to the developers.

Whatsapp also often blocked users using those apps (I had it happen multiple times) and you could reactivate your account if you logged in with the official whatsapp.apk again. A few days later the Sailfish apps were updated and I would switch to one of those again :)

So now there is no other option then use the whatsapp.apk, or just not use it and switch completely to Signal.