That's the elegant version ! We had two single beds bound together at the legs and a mattress topper over the whole surface. They could be used without topper and disconnected.
When I hunted for a new, better mattresses in the South of France, it was impossible to find the same sizes. The single mattresses were shorter - must be some crazy notion that if you are single, you are short but when you are a couple, you grow. (You do grow, but not litterally, in size).
Finally I found the mattress I wanted, as long and as large as my two old ones together. No more separations. I got a single folding out chair from Ikea which came handy for a father with daughter booking.
Maybe you should add the foldout in the living room after all - one kid can go to bed and the other fall asleep before the tv, that's what they mostly do at home.