Help transitioning to floor sleeping

Long story short: i have to change my sagging current mattress. But before spending thousands on a new firm mattress, I’d like to give floor-sleeping a chance. Also, I’ve been watching a Korean series and it seems sleeping on the floor is common.

With that said, what should I buy to begin this journey of sleeping on the floor? I’ve read about tatamis, shikibutons, and futons.

How should I start?