LoL 65" is too big for that room and you want to fit a 75"?
Welp THX says otherwise, for the distance we'll be from the screen in here, they recommend an 85" and say a 75" would be the next best size for viewing. I mean the TV will be mounted on the wall, it's not like it's going to take up valuable space.
I have a 55" and it's definitely too small, we watch at about 9.5 feet away and subtitles are really hard to impossible to read on most movies. Let me ask you, is there any difference between a living room and a bedroom? I mean aside from the bed of course. I looked up a dozen different room-size calculators for TV's and almost every one recommended a 85" from a 9.5 foot viewing distance.
Will it look huge on the wall? Probably, but it'll also provide the most immersive movie experience. On the flip side not a single one of the sites recommended 55" (and I totally agree) There are a ton of people on avsforums who have 85" tv's in rooms even smaller than this.
Your girlfriend sounds sensible. You should listen to her.
Sensible? Her 32" TV's 14 feet away from her bed (where she watches) THX recommends 4 feet for a 32". She knows absolutely nothing about audio or video. She thinks it's gonna be too big because of her complete lack of understanding, I showed her 8 different sites that said the same thing I told her, yet she still thinks I should get a 32" If I listen to her I might as well not even have a TV, watching shit on a 32" from almost 10 feet away will further wreck my already bad vision.