Look at the Six Moon Designs Meteor Bivy - you can download the pattern and make it, or order one. Also check out bugnet shelters to pair up with a tarp - there are one and two person models around. Seen those at REI for not very much money.

It's interesting how I used to be so very concerned about creepy crawlies and have found that it isn't so much of a problem as I used to think. I have yet to wake to find things crawling on me for all the nights I've spent under a tarp without a net. Not parking myself next to rotting logs or in foliage really cuts down on the bugs. There are some locations where you can't get out of grass - that's where I take a full tent or hammock setup. On duff or rock in late summer I don't worry about it.

For the worst part of mosquito season I use a fully netted/zippered hammock - for someone who dislikes things crawling on them, a hammock with net is ideal - treat the straps with permethrin and nothing will crawl down the suspension, treat the bottom and nothing will land on the hammock fabric.

Never had a snake anywhere near me while sleeping. Never heard of anyone having that problem, either. I had a mouse under my tarptent once - on Angel Island, where it's not even what you could call backcountry camping and the animals actively seek people in search of scraps.

Tarptents for two people can be pretty light and roomy, and excellent bug protection. I believe you can download a pattern for the original two person tarptent as well.