I think most people tend to use ink or similar when journalling. I tend to prefer pencils. To be specific, 2mm lead holders. This is the same lead size as a regular wood and lead pencil. I also use 2H lead which is a bit harder than the more common HB lead and does not smudge as easily (I am a leftie). Some brands I use are Parafernalia, Troika, YStudio, and Faber-Castell.

I recently treated myself to a Kaweco Aluminium Special Mini 2mm Pencil in Matt Black. It came in a nice tin (which I plan to use to keep extra lead, erasers etc) and is a handy size. Not too small to be functional. I have a little leather Kaweco pen holder to keep it in.

I bought this from Cult Pens. I am a frequent shopper there because of their range and their prices (this one was 25% off).