I purchased a Knox Next Cardboard for phones up to 6.2″. Knox labs does a great job on the design with tapered edges. I use it with my Samsung Galaxy Note 4.
I’m still not a believer in Google Cardboard for VR though. I understand it brings VR to the masses for super cheap but overall it’s a bad VR experience. Distortion usually isn’t correct and tracking typically stutters. Could just be my phone but it’s buttery smooth in my Gear VR. People should be cautious with VR and Cardboard. VR today is much better if you spend the money to get some decent gear.