Thanks to LifeHacker I found this useful app called Type2Phone. I always loved the way iMessages could be send and received on the iPhone and via Messages app on the Mac aswell. For writing notes, reminders or messages on WhatsApp I still had to type directly on the iPhone. With the help of Type2Phone this is no longer necessary and I can type on the iPhone as fast as on the Mac!
After pairing the iPhone with the Mac via Bluetooth the app sends any keyboard input immediately to the iPhone (of course only if you click on the app and not when it's in the background ). It works incredibly well and it's also possible to send special commands e.g. to emulate pushing the home button, turning brightness up/down, lock the screen, play, pause, volume control, etc. Very useful is that the well-known shortcut CMD+A for selecting the whole text works aswell. A quick copy and paste on the iPhone is possible without a problem.
It is free until Sunday, so be sure to get it today. By the way: The app works with any smartphone that supports Bluetooth keyboards and therefore it can also be used with Android phones.