I’ve been using  onyoutube.com/en for exactly this lately and it’s been great. It is a super straightforward web tool where you just paste the link and it handles the conversion for you.

The quality is actually impressive—you can get high-bitrate files like 192kbps or even higher. It’s free, very fast, and doesn't have those annoying pop-ups that most converters do. It’s definitely my favorite for building a clean offline collection. Give it a shot!