According to the docs fzf can integrate with tmux for the terminal splitting. That's probably easier, just use screen or tmux to run your script in one pane and a regular terminal in the other. But if you do want to reinvent the wheel, then yea, Curses would be one way.
Comment on Re: textual GUI using only part of the terminal
Are you positive that Curses can do that or are you only guessing?
Other guy mean that tmux is created using libevent and ncurses -- can you reinvent a terminal multiplexer using perl and curses? Sure theoretically, but it is a lot of work in all all corners of the environment