Just as a FYI, here are the general rules of DOF:
For thicker DOF, use a tighter aperture and/or shorter focal length and/or further lens-subject distance
For thinner DOF, use a wider aperture and/or longer focal length and/or closer lens-subject distance
Tricks can be played to manipulate DOF. Easiest, with only slight loss of IQ, is to use a strap-on adapter. A +1 dioptre meniscus, available in any cheap set of closeup adapters, will shorten the working distance to 50-95cm / 20-38in. This turns even the DA18-55 into a portrait lens. I can turn a not-too-fast 50/2 into a 75/2 portrait beast by adding a good (yet cheap) 1.5x front adapter -- Sony and Olympus are probably best. My Sony VCL-1546A cost all of US$4 shipped.
Bokeh depends (among other things) on number and shape of the iris blades; aperture size and placement; the lens' optical formula; and relation of background to subject, both distance and light. A brighter background emphasizes the bokeh. Few or uneven iris blades can give harsh bokeh and that's not always bad -- I like smooth bokeh with complex subjects, and busy bokeh with bland smooth subjects.
And preset-aperture lenses, where the iris is near the center of the lens, render bokeh differently than do similar auto-aperture lenses, with the iris near the back of the lens. Case in point: I have two CZJ Tessar 50/2.8s, one a little silver Exakta-mount preset with 12 iris blades, the other a big black M42 auto-aperture with 5 iris blades. Same maker, same formula, but quite different results. Or I'll compare two M42s, the Meyer Trioplan 100/2.8 (preset, long lens, 15 blades) vs the SuperTak 105/2.8 (auto, tele group, 6 blades). The SuperTak is nice. The Trioplan is a bokeh monster.