Passing layer sourceText into double quotes of an expression?

I'm building a template to display data from a csv. The user will type the name of a column into a text layer, and this string is passed into the expression to display data from this column. However I can't figure out how to pass the sourceText of the text layer into the csv reference expression. I suspect I'm just using double and single quote wrong, but can't seem to get it. Any idea how to pass a string into the double quotes of an expression?

colName = thisComp.layer("Type Col Name Here").text.sourceText;
thisComp.layer("Population2019.csv")("Data")("Outline")("'colName'")("'colName'" + " 0").value);