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Try F# my man. In my experience its the best option for a statically typed functional language if you want to actually get stuff done and not just dick around. Also as you're coming from C# it would be the logical choice since the tooling is all there and you're already familiar with it. Visual Studio Code + Ionide plugin is what I use. I really don't understand why F# isn't more popular. Maybe it has something to do with its Microsoft roots making it uncool among the hip functional crowd?

If you like C#, have you tried F#?

Check out Kotlin, it might meet your criteria.

Haskell's compiler can defer type errors to the runtime. You can run your partially checked code.