To add more space, use

\, for a thin space \\( a \, b\\);

\; for a wider space \\( a \; b\\);

\quad for even wider \\( a \quad b\\); and

\qquad for extra wide spaces \\( a \qquad b\\).

To set plain text, use \text{…}: \\( \lbrace x \in s \mid x \text{ is extra large} \rbrace \\).
You can nest $…$ inside of \text{…}.