The Vantage seat definitely would be a good option. Along with the lumbar support you can put the seat way back plus the knees up for support. I'm big so when I tried it out I didn't want to just "whoomph" down on it and the height of the chair helped both up and down. You would probably want to look into the h-bar for assistance/control (less jerking) and a note that the armrests are lower than expected, they won't be that helpful getting up/down.
Another thought would be rigging up a head support like I've seen on the Native Watercrafts. I am betting it would help a lot even if you don't think it's necessary - it would be a bit of pressure off the neck on down - less stress if you are out for awhile. I am sure I've seen them on recumbent bikes too and that's your position if you want to lean back and paddle.
Good for napping too, I bet
. I'll definitely be trying to jimmy one up if/when I get one.
I'm sure I saw a YouTube video on just the seat if you want to see the range before checking it out in real life.