Welcome aboard! I'm another new member who just recently found this site. Can't really help you directly on your specific question, but here's some general response.
There are frames that can be adjusted for a sitting position, I have a friend who uses one because of physical issues. She has an office type chair on wheels and a long/industrial chair mat. She isn't using a long arm machine, her throat can only take about 9", but that's still a lot easier on her than trying to handle a full sized quilt without the frame. She says the biggest drawback for her is that she can't do even a baby quilt really with minkee on the back because it makes the roll too big. Her basic setup is narrow, can't walk around it but it fits in the extra wide hallway/landing that is overlooking her living room.
There are also industrial chairs (not cheap) made for/used by the standard height frames -- but then again you would run into the space constraints.
The set-up I use belongs to my tall friend... it is a hardship on me physically but hey -- I have access to a long arm so I pay the price in my body the day after I use it. It's still a lot less than trying to do them on my little old sewing machine and I can get better results faster.
I would say no matter what you get, a stitch regular is required. Sure, some people can do it without one but then people do a lot of crazy stuff. If you can get one that works in the space you have, a computerized system that can do some of the work for you is ideal in my opinion.