I booked a trip last night as a BA Holiday that involves me flying Edinburgh to Vienna, staying in Vienna for a few nights and then on to Bratislava for a conference. My wife is coming out on a separate, flight-only, booking for the Vienna stay and then heading home as I get the boat to Bratislava. I can see in the OP’s position that the hotel might only offer a single room, but usually you get a room type choice and would you not normally get a double room offered?

Interestingly I added the breakfast offer on to the rooms and the Ts&Cs said that the included breakfast was for up to two people.