At the moment I have the ‘login required’ setting enabled so it is necessary for users to have an account to view any content on the website, however I was wondering if there’s a way (or a plugin) that would allow me to change individual posts to be publically accessible?
The easiest way would be to have a publicly accessible category (you can control these permissions within a category’s settings) and make the other categories require users to be logged in. You’d want to setup your category permissions first, and then disable the “login required” setting. There is a theme component that can also allow users to preview categories they can’t access: Category Previews
Just to clarify, will this work for individual posts or only for whole categories?
Whole categories; permissions in Discourse are handled by groups and categories and can’t be applied to individual topics.