A bivy for rain protection (a splash bivy) is not necessary for a solo person under a two person tarp. In my experience, I am colder with this type of bivy than without because it compresses the down around my butt when I sleep on my side. If you are worried about mosquitoes, you can get a Sea to Summit nano net which is very light and gives you a relatively large amount of livable space. It’s also quite fragile. Don’t let any velcro get near it.
Backpacking Light community posts are moderated and here to foster helpful and positive discussions about lightweight backpacking. Please be mindful of our values and boundaries and review our Community Guidelines prior to posting.