A ball point pen is a ballpoint pen. Fine if you're just sketching on any odd paper (which you seem to be if you're using stuff with lines on.) Fine line permanent ink pens you can buy at most department stores or art shops are favoured by most because you can paint over them without blurring the ink. Check the internet and you'll turn up dozens.
Indeed, indeed, Repentance oft before, I swore---but was I sober when I swore?
And then and then came Spring, and Rose-in-hand, My thread-bare Penitence apieces tore.