I use Prometheus + Prometheus Alertmanager + Any Free Tier paging system (currently OpsGenie, might move to AlertOps).

Having a feature-rich TSDB backing alerting minimizes time adding alerts, and the UX of being able to write a potential alert expression and seeing when in the past it would fire is amazing.

Just two processes to run, either bare or containerized, and you can throw in a Grafana instance if you want better graphs.