A bit late. Author of nine here. There is also nine_cowboy, as it might be relevant since you are using Cowboy. It can help reduce some of the boiler plate that the default Cowboy setup uses. I used it for a toy Rock Paper Scissors app I was working on and found it worked quite well for both HTTP and Websockets. It also uses my sql migration library strata, which might be helpful for you. Besides that I made these libraries, I prefer simple components that I can put together to build my own framework with.
Since frontend isn’t Erlang’s strong suit there are less options. The new framework Arizona is working on replicating Phoenix like behavior. Perhaps that is more inline with what you were thinking.