Hi @adampuddicombe,
Thank you for your question.
You can achieve this by using custom CSS solution posted in the following topics.
https://colorlibsupport.com/t/how-to-make-only-one-post-full-width-and-the-rest-in-grid/#post-58491
https://colorlibsupport.com/t/a-few-questions-how-to-make-only-the-first-post-full-and-regarding-font/#post-59417
If the custom CSS solution doesn’t work on your site then could you please share me your site URL where you are using it so that i can troubleshoot it?
Best Regards,
Movin