How do I know if I should choose extra-firm instead of firm or medium-firm?

Ask yourself if your current mattress feels too soft, saggy, or unsupportive even if it's already firm. If you primarily sleep on your back or stomach, prefer a very solid feel, and don't mind a harder surface, extra-firm could be a good fit. If you're uncertain or occasionally sleep on your side, firm or medium-firm is usually a safer and more versatile choice.