Your post title mentions SFTP but are you really wanting FTPS? There is a difference!
Have you talked to your site support group? Usually securing FTP means implementing digital certificates and few, if any, sites allow application programmers to add digital certificates to RACF (or whatever security package your site uses). In fact, your site support group can tell you whether or not it is even possible for you to use secure FTP on your system -- it is NOT required (at this time) to have it installed on z/OS, and some sites don't have it at all.