If you want a fountain pen, try the Super 5. It's inexpensive, and it can handle waterproof inks for sketching + colorizing. Converter available, so you can use any ink you like (the Super 5 ink is quite expensive).
https://papierlabor.de/en/shop/pens/super5-m-fountain-pen/
A good waterproof ink:
https://www.rohrer-klingner.de/?page_id=1063&lang=en
I went to see it is very interesting. Thanks so much and if I try I will show you.