For Evil users, user @doyougnu suggests binding your local leader to , (instead of the default, \), which frees up \ to be used as entry into Symex Mode. This is convenient as \ feels like another Esc but dedicated to Symex mode instead of Normal state. The drawback is that , is an otherwise useful key in Normal state (for in-line repeat search backwards). Although, using it for the local leader is a widely used pattern by Vim and Evil users, and if you are one of them, then this might be a good option for you.
With this option, entering Symex from Normal state is convenient, but you’d still need to visit Normal state on your way to Symex mode from Insert state. If you’d like to avoid this, See Escaping to Symex Instead of Normal State.