How to sound-proof a room with minimal budget
I would start with an area rug to cover most of the floor.

Hanging tapestries on the walls and door can add to the decor and help deaden the sound.

Do you have access to the underside of the floor from below? This would be the spot to add insulation.

The problem with lower frequencies (male voices) is they resonate the building itself and are more difficult to block.

Good luck!