I would suggest the Pfaff Passport. It has built-in dual feed (IDT) since smooth feeding is your top priority. It's lightweight, has serpentine stitch, and all the other nice features you're looking for.
As an aside, do you have an over-bed table? One with wheels, like in the hospital. It might be easier on your legs than setting the machine on the board on them. I was looking at them a few years ago when my dad was sick, and you can get one for under $100.
Good luck with your search!