No you are not missing anything but 1 convo and 2-5 nights sleeping in Ann's bed without sex and that is all there is to sleeping with mom.
She will never allow you to have sex with her and sleep in her bed at the same time.
So after a break I tried following your instruction and it didn't work, I look at the walkthrough and your post and I wanted to clarify the timeline of event.
You get rid of eric--- money issue breakfast arise----you get the "I know what I want option" and pick the I want to sleep in your room---nothing happen until after the first movie where you pick the I want to sleep with you option before talking about the moovie with Ann----- then you have the 2 night sleeping with her, once all of that is done you can move on with the rest of the storyline.
Edit: nevermind apparantly the one crucial step you need to do is quite simple, after the movie with Alice about smoking, simply talk to Kira so she leave Ann's room, then talk to Ann but do not talk to her about the movie, simply go back and forth once and that night go into her room.