Another option is to do the actual drawing with pen(cil) and paper, and then do digital inking with the mouse. Either scan the picture or take a photograph of it with a smartphone, then draw over it with an inking brush, with Krita’s stabiliser enabled to smooth out the lines a bit. Inking’s easier to do with a mouse because you can zoom in and get a bit more forgiveness with your linework. Another thing you can do is work at much higher DPI and scale it down when finished, which will smooth out a lot of imperfections. That should help a bit as well.