I understand your pain.

I used to have sensu, but it was a pain to keep updated (and didn't work that well on old rpis)

But what I did find was a good alternative was telegraph->some sort of time series (I still really like graphite, influxQL is utter horse shit, and prometheus's fucking pull models is bollocks)

Then I could create alert conditions on grafana. At least that was simple.

However the alerting on grafana moved from being "move the handle adjust a threshold, get a a configurable alert" to craft a query, get loads of unfilterable metadata as an alert.

its still good enough.