When I hurt my back I bought the smaller containers of Tidy Cat also 14lbs. It doesn't clump so well though so now I switched to Fresh Step which unfortunately comes in 25lbs (it's still in my car). The kitties seem to like it better than Tidy Cat. I would avoid the "lightweight" litters as there have been reports of them causing respiratory problems in cats. My friends cats had problems with it (she bought lightweight litter when she broke her arm). There's also litters made of walnuts and coconuts that are lightweight but I do worry about allergies. Good luck in your litter hunt!
Also, Dr. Elsey's is a good litter. It comes in 18lb bags.