Mailplane has been my go-to--it's basically a native wrapper around Gmail, but has integration with a number of popular Mac apps and native-style keyboard short

Mailplane has been my go-to--it's basically a native wrapper around Gmail, but has integration with a number of popular Mac apps and native-style keyboard shortcuts and easy account switching if, like me, you have multiple GApps/GSuite logins. Kiwi is similar, but doesn't have quite the level of integration Mailplane does although it has a more modern interface. That said, I missed extension interoperability with Gmail enough that I largely just access the Gmail website directly through Chrome or Safari now.