If I was using natural light by a window, I'd use XP2 Super 400 or one of the other C41 processable films as they have lovely fine grain and superb detail. I saw some studio lit portraits shot on Fuji Acros 100 which were awesome, so I'd use that if there was sufficient light. Shooting Kodak Portra 160 (or 400) in colour and then doing a mono conversion would give you options.
I'd avoid filters altogether, these days and have a play in Photoshop if you're printing on an inkjet. However, if you have an old UV / Daylight filter that you're prepared to "ruin" you could smear a tiny dab of Vaseline / petroleum jelly onto it. If used sparingly, you'll keep all the detail and sharpness but you'll get a lovely soft "glow" which will smooth out a lot of lines, wrinkles, thread veins etc. Alternatively, I used to use a pair of sheer neutral coloured ladies tights, stretched over the lens, to create a soft focus effect.
Have fun, experiment......
