Why don't you try a mechanical pencil? A small diameter like .5mm is silky smooth, easily refillable, erasable, and you can get a nice ergonomic drafting pencil like a Pentel GraphGear, which feels really good in the hand.
The only mechanical pencil lead I've found that matches the smoothness of a good rollerball or fountain pen is Pilot Neox in 4B. Although it's my favorite pencil lead, it has the significant disadvantage of smudging easily.
They've got the pros of both mechanical and standard pencils without the flaws of both. I use one for writing and sketching and i've had the same pencil for 12 years now and still use it to this day. The refills can be a bit tricky to find though in stores. Art supply stores sometimes have them and i've seen them at places like staples.
When I was in high school, I bought a .9mm mechanical pencil, and it was glorious for standardized tests. Filling in circles was just a quick spiral inward, and the forms with rectangles were even easier — just a swipe across. I still have the thing, even though I haven't taken a multiple choice test in over a decade.
