SQL Server

That is not a typo. Microsoft has ported SQL Server to the Linux platform. A SQL Server in a Docker container running on Ubuntu can be spun up in just a minute or two. I have seen a few SQL Server installations in my day, but none that were quite that fast. Simply choose your desired SQL Server version, and run the corresponding docker command. So, for example, for the latest 2017 SQL Server, simply run, after changing the password, the following

docker run -e "ACCEPT_EULA=Y" -e "SA_PASSWORD=yourStrong(!)Password"
 -p 1433:1433 -d mcr.microsoft.com/mssql/server:2017-latest

So will DigitalOcean offer managed databases with SQL Server? Due to licensing issues, I would say this is highly unlikely. Nevertheless, if you are unwilling to migrate your databases from SQL Server to PostgreSQL or MySQL, you do have the option of running SQL Server in a linux container in the cloud.