Welcome to the forum.
It's never worth booking tickets on trainline. Despite their advertising they don't have access to cheaper tickets and they're never cheaper as they add a transaction fee. Simply use a train operating company website, some like Virgin even use trainline's software so the user interface will be identical. Train companies can sell each others tickets (although a handful of special offer tickets might only be available on the website of the company you're travelling with) and are not allowed to charge booking fees.