best email client for legacy macs - adequate filing and organisation tools

Been using Apple Mail so long but it's starting to feel inadequate because I really want to organise conversations in folders and there is such limited space to do this.

Is there a better free mail client for mac that will run on Mojave 10.14.6? Or even a paid one, if not too pricey.

Or am I missing a great way of organising everything without moving mails out of the Inbox?

Either way, I know it sounds kinda basic, would be really glad of advice.

Thank you.

Paul V