Oh, I had forgotten about sleeping with Sigrid! If you follow Hadvar, Alvor and Sigrid invite you to stay with them. Then like you said, Alvor hops into the single bed. Welcome to Skyrim, would you like to sleep with my wife? Those two are so hospitable.
Also there’s this greeting from
Nivenor of Riften: If you’re looking for a handout, you’ll want to speak with my husband. If you’re looking for
company, I suppose I could do worse.
I think it's the Skingrad Mages Guild in Oblivion. They play musical beds all night long.