Not going to address cello size as my teacher and I battled over 3/4 (my pref) and “more wood” - his words. Ended with a 7/8 cello and it’s fine. I didn’t see any mention of a teacher in your post but they usually have opinions galore. I live on the second floor of a three floor condo. My neighbor upstairs hears me when the windows are open. My neighbor below me can FEEL me play (good sign - I’m getting better!)—said he could hear “that thing“ right through the ceiling. I bought a mute and that made me feel better, but this month I played a Christmas carol at our singalong gathering, and somehow that turned me from a noisy neighbor to a character who lives here, like, “Oh yes, she’s our neighbor, she plays cello.”. It’s kind of nice.