I would look at one of the "Chariot Warbird" tubes such as the Chariot Warbird 3. This is a great sit in style tube with a backing and lots of grip handles. It's very stable and hard to tip. The Warbird 3 is a three person tube yet one person can sit in it easily and have fun. I personally like the three person tubes better as they are bigger and handle waves better. I got mine at Sams club a few years ago for real cheap money. Here is a picture of one at Overtons...
http://www.overtons.com/modperl/prod...4&merchID=4006
You may want to call Sports and Marine Parafunalia in Gilford. If they don't have it I bet they can order it. They are real good people there and have lots of lake toys and towables.
Good Luck!
Dan