The
Holiday Inn Munich (
not the city center one) allows four adults per deluxe room and has two 1.4 meter (??) beds in this room. I guess you could push them together as well. Maybe call the hotel in advance. Not comfy king beds, but "feasible", imo. Worked fine for two adults and two teenagers that I booked in there. Con, it's not very centrally located and doesn't have good public transport options.
Do 3 meter beds exist?
That being said, I had to google poly couple... Enjoy your stay!