As much soft stuff as you can... Rugs, large pictures, curtains, soft chairs, etc.
We have similar, and it isn't so much the echo but the whole environment is "noisier" - can't think of a way to explain it , so two convos in the room are harder, kids are amplified etc.
It's obviously worth it for the impact of the room, and how special it is as a space... But everything in life has a drawback...