In reply to harveybirch96:
Bivy's are great for fine weather, no midgies and for places where it would be hard to put a tent. Bivying in the wet, particularly for several days requires a certain strength of character. You will get damp (condensation and getting in and out). In strong wind and heavy snow the bag will compress down insulation. As soon as you think about carrying a tarp as well, you might as well have a tent. In bad weather you 'wait' in a bivy rather than 'relax/live' in it. Remember all bivies are bit like waterproof jackets once thier repellancy wears off and the face fabric gets soaked breathability drops significantly. Bivvies will survive conditions where tents won't. Whether you will function well after the storm is another matter.
One man tents weigh little more than hooped bivies, offer more comfort; cooking, reading, getting dressed, siting up, storing gear and stay drier. But lack the view and feeling of being 'out in the landscape and the elements' and have limits as to where you would want to use them.
In short thier is nothing like a high bivvy in good conditions, but equally wet weather bivvies will be memorable......
With a solo tents you have to decide if you are happy with a mesh inner (3 season use) or want to use it in winter, and how exposed some camp spots might be; so how light or robust it can, or needs to be.