Martin, before you follow the advice with Dektol and higher temperatures: be aware that these techniques most likely diminish the low contrast effect you were looking for to begin with.

If you want the same tonal result but more grain, you need to crop your image. Use a shorter focal length than you would normally choose and use only part of the negative for enlargement. If you use the center region of your negative area, you use the sharpest region of your lens, so your images will look just as sharp.