I don’t know why it’s not even advertised on the Ghost self-hosting page, but I have an idea…
Usually companies that offers referral programs are massively overpriced, and they just sucks. Look for the VPNs, most of them have all referral programs. You should search for the ones that don’t have it (like IVPN) 
I had several problems with the Digital Ocean Ghost updates, especially when I had to update Node JS recently. It was a complete mess. And if while updating you minimize the Digital Ocean CLI, it will stop and crash everything. Also if you choose the 1GB RAM Digital Ocean it will crash out of the box (like described in this thread). I really had enough…