The key to cornrows is simply doing French braids on a carefully planned hair pattern. Thick cornrows are simply thick French braids also carefully created on a planned grid or hair pattern.
Traditionally cornrows, which are braided very close to the scalp, using an underhand, upward motion to produce a continuous raised off-the-scalp plaited row are often designed to form a series of straight lines which flow from the hairline to the nape of the neck.
They can also be formed in geometric, curvilinear or other patterns.
While cornrows are normally very tightly plaited, their are other options to weave them looser to make them more comfortable.
I had my entire head cornrowed when I was in Cosmetology school. Not only did it hurt while they were braiding my hair because they pulled the braids so tight, it hurt for days afterwards. It was also difficult to sleep.
Ultimately I only kept my braids in for one week because of the discomfort. Many people don't talk about that aspect of wearing braids or cornrows.
I also a small section of my hair done in dreads, to try it out, and it doesn't hurt at all compared to cornrows. Dreads might eventually hurt if they are twisted too tightly, but if kept loose, they are much easier to deal with.
If you want to try cornrows, why not start with just a small section of your head. It's very fashionable to have just part of your hair braided with the rest worn flowing free. Just a thought.
Good luck to you.