PSA: There’s a great alternative headtracking program and it’s free! Only requires a simple webcam.
It was posted by another user a while ago. 
I’ve been using this and while it requires some tuning and adjusting the sensitivity, it’s an amazing addition to the experience!
Proper TrackIR is probably still better and smoother, I don’t think you have to feel bad about spending the money for it, but Opentrack + AI Track is still amazing for people who can’t or don’t want to afford an expensive headtracking setup. 
(Note that you might have to try different versions of AI Track. Don’t give up if it doesn’t work the first time around)