Have you looked at hiking/camping stools/chairs recently?
Modern materials and designs mean that these have become prettty lightweight and compact while still being sturdy.
They are not going to be suitable for everyone, some are a bit too low, but you may find one that suits you.
Take a look at your local outdoors shop they should have a few you could give a try.
I like this one, weighs about the same as a bag of sugar and folds up to about the size of roll of wallpaper.
http://mywildearth.com/hiking/portable-camping-stool/
There are other lightweight portable seats on that website.
http://mywildearth.com/hiking/lightw...chair-reviews/