If he already has the phone, then the Samsung "headset", which is really just a holder, is the best solution - as it's designed for the shape and fit of the phone.
There are generic alternatives, search for Google Cardboard. They take a bit more fiddle to get working, but the end result is the same.
Google's Daydream is the top of the line holder right now... really what makes the difference is the motion sensitive wireless controller it comes with. Not sure how many phones it works with, however it's designed for the Google Pixel.