Are you producing a thesis, and trying to obey regulations that were drafted in the typewriter era? Or are you producing copy for a journal that insists on double spacing for the submitted articles?
LaTeX is a typesetting system, so the appropriate design conventions are for ``real books''. If your requirement is from thesis regulations, find whoever is responsible for the regulations, and try to get the wording changed to cater for typeset theses (e.g., to say ``if using a typesetting system, aim to make your thesis look like a well-designed book''). (If your requirement is from a journal, you're probably even less likely to be able to get the rules changed, of course.)
If you fail to convince your officials, or want some inter-line space for copy-editing:
\baselinestretch:
\renewcommand{\baselinestretch}{1.2} may be enough to give
officials the impression you've kept to their regulations. Don't try
changing \baselineskip: its value is reset at any size-changing
command.