There are several very light tents that weigh as little as a heavy duty hooped bivy, but offer more space. Tarptent, Lightheart, Six Moon Designs come to mind.
Something like these -
Tarptent Contrail
SMD Lunar Solo
Lightheart Solo

Granted, finding a used one may be a challenge, but well worth looking for compared to a bivy, in my opinion.


Edited by TomD (04/22/14 09:58 PM)
_________________________
Don't get me started, you know how I get.