tmls is a CLI overlay for tmux ls that facilitates selection and attaching of sessions. Navigate active sessions with ↓/j and ↑/k, select one by hitting enter, or cancel with ctrl+c or q.
Development
You'll need Go (I recommend using 1.10) and make. Get the source via go get github.com/fallafeljan/tmls, navigate to $GOPATH/src/github.com/fallafeljan/tmls and build with make. Running make install will trigger go install, which makes the binary available to your system.