What are best practices for migrating a Next.js JavaScript project to TypeScript

I have a Next.js project built with JavaScript, and I’m considering migrating it to TypeScript.

My current project setup:

Next.js (version 14)
Tailwind CSS
shadcn-ui components
JavaScript (no TypeScript configuration yet)

My specific questions are:

What is the recommended approach for gradually converting .js files to .tsx/.ts without breaking the existing functionality?

I am no big expert of TypeScript. Are there any automated tools that can help with this migration? What are the critical files that should be converted first?

I have read two Stackoverflow’s posts on the topic:

  1. Converting Next.js – Javascript code to Typescript
  2. Converting Typescript to Javascript Best Practices

But these posts tackle narrow usecases, while I want to consult on the approach related to the Next.js project written in JavaScript.

Also I’ve reviewed the Next.js documentation about TypeScript but didn’t find the answer.
So, I would appreciate practical advice from developers who have done similar migrations.