Feel free to use my (open source) Todoist backup tool[0], which doesn't require a premium account and which is even more powerful than the built-in premium option. You can both export more data and use a format which is more suitable for data processing. Read my blog post[1] for more information.
[0] https://darekkay.com/todoist-export/
[1] https://darekkay.com/2014/12/14/todoist-export-tool/