My setup is an Zpacks Altaplex tarp (7.5 oz) which provides 360 degree rain protection and a Zpacks bathtub groundsheet (3.5 oz). A bathtub groundsheet will provide good protection if water does pool underneath because of bad site selection plus it provides good splash protection. I prefer a tarp like Zpacks Altaplex tarp as I don’t have to worry about which way the rain or wind is when I set up camp. It provides very good 360 degree protection.
While I carry a headnet, I usually don’t use it in the night as I am fully covered head to toe while sleeping. And treating my tarp with permethrin usually kills them throughout the night if they get caught inside. I usually spray some extra permethrin at the top where the pole is which is where they are trying to get out. Most of the mosquito’s disappear when it gets dark. If you are the kind who gets to camp early and hangs out at camp, then you may have to deal with mosquito’s till it gets dark.
I have used a bivy – but, I think it is redundant and adds weight. Usually I end up using up the tarp as it always seems like it is going to rain:-) I have decided to ditch my bivy and just use the tarp all the time.