Buy extended support licenses
Extended Security Updates via Enterprise and Enterprise Subscription Agreements provide “critical rated security updates and bulletins” and will be applied immediately after 9 July 2019. These updates are only available for three years up until 2021 when they will cease.
Lift and shift to Azure
You can migrate SQL workloads to Azure virtual machines straight away and apply regular security updates. After 9 July 2019 you will get free Extended Security Updates, ensuring continuous security support.