Use - free when a sentence refers to something that was never present, for example a carefree child. I use the denotation because while -free tends to have positive connotations, -less can have either positive or negative connotations. But using the above rules based on context works in most situations.

word choice - When is "-less" used, and when is "-free" used? - English ...

6 For free is an informal phrase used to mean "without cost or payment." These professionals were giving their time for free. The phrase is correct; you should not use it where you are supposed to only use a formal sentence, but that doesn't make a phrase not correct.

grammaticality - Is the phrase "for free" correct? - English Language ...

If so, my analysis amounts to a rule in search of actual usage—a prescription rather than a description. In any event, the impressive rise of "free of" against "free from" over the past 100 years suggests that the English-speaking world has become more receptive to using "free of" in place of "free from" during that period.

"Free of" vs. "Free from" - English Language & Usage Stack Exchange

The fact that it was well-established long before OP's 1930s movies is attested by this sentence in the Transactions of the Annual Meeting from the South Carolina Bar Association, 1886 And to-day, “free white and twenty-one,” that slang phrase, is no longer broad enough to include the voters in this country.