hello :>
this template might help you with mapping :
me personally i use this one, looks a bit complicated but helps alot for me
you might wanna try Photoshop alternative softwares, GIMP, and Krita are some of well known open source softwares, maybe Photopea if youre used to Photoshop, or Inkscape if you're into vectorized style. Personally i think vector style is worth to learn if you dont own any pen tablets, feel free to hmu if you need a bit help, i'll help as much as i can