Single quotes do not expand the $variables inside them.
Try
'{"item":"'"$SOMETHING"'"}'
instead. Brief explanation:
'{"item":"' is a string delimited by single quotes that contains double quotes"$SOMETHING" is a string delimited by double quotes, that expands the variable $SOMETHING'"}' is again a ''-delimited string that contains double quotes- Simply writing those strings in a row without gaps is string concatenation
In this way, you get your variable expansion, but don't have to insert any backslashes to escape the double quotes.
