I see you regret Datadog but there's no alternative - did you end up homebrewing metrics, or are you just living with their insane pricing model? In my experience they suck but not enough to leave.
Not author but Prometheus is perfectly acceptable alternative if you don't want to go whole Otel route.
Currently going through leaving DD at work. Many potential options, many companies trying to break in. The one that calls to me spiritually is: throw it all in Clickhouse (hosted Clickhouse is shockingly cheap) with a hosted HyperDX (logs and metrics UI) instance in front of it. HyperDX has its issues, but it's shocking how cheap it is to toss a couple hundred TB of logs/metrics into Clickhouse per month (compared to the kings ransom DD charges). And you can just query the raw rows, which really comes in handy for understanding some in-the-weeds metrics questions.
VictoriaMetrics stack. Better, cheaper, faster queries, more k8s native, etc. Easy to run with budget saved from not being on Datadog + attracts smart and observability minded engineers to your team.