Stone you dont' mention which camera system you are using.
I agree lighting is a big factor. I prefer actual soft lenses rather than the filters that were much abused for normal portraits in the 1970's/80's. Much practice is required and you can't see the actual result on the groundglass when using a soft focus lens; something close to it yes, the actual result come from experience not wysiwyg. Particularly the detail might be too little or much until you display it at the intended final size. An old soft focus lens on LF would be my choice because that's what I have. I like the Kodak 305 portrait and Reinhold's wollaston meniscus 190mm lens. I'd use the kodak at about 6.3 and the wollaston at f8 for a head and shoulders softly lit photo. I've use pentax's 67 and soft focus, but not enough to promise results. I've seen other people's excellent work with hassy+imagon combinations.