My struggle now is trying to figure out a good class balance for him... Why can't there be a draconic warlock.

If 3rd party content is an option. There plenty of options out there, Like Kibbles has a free dragon patron www.kthomebrew.com/thelist

Compiled Homebrew List — KibblesTasty Homebrew

Expanded list of subclasses for D&D 5e. A Link Hub for new player options with content by KibblesTasty, Griffon's Saddlebag, and more.

Captain I found an alternative Warlock supplement if you want itttt