Question about converting child theme

Hello,

I’m in the process of creating a child theme for my website due to receiving a lot of recommendations from other web developers. We hired someone outsource that designed the website and did custom coding in the parent theme and I was told that was a no no. Luckily we’re using a web hosting company that keeps automatic backups for the site though I still want to convert the site into a child theme.

I used a child themify plugin and the website does not look exactly the same as before. From what I heard, when you create a child theme, it’s supposed to look exactly the same as your parent theme but your css will become a child css and I would have to manually put in the php files that I want to edit.

Is this normal for a website to break up a little bit after a child theme conversion? Or should I just try a different method?

I’ve had a lot of trouble with this conversion, so if anyone can tell me the easiest way to do this without breaking anything I would really appreciate it. Thank you so much