Batting is a modern invention. Our grandmothers and great-grandmothers used to quilt the top straight onto the back all the time. I know, because that's how my great-grandmother taught me how to quilt. If they needed batting, they were lucky to be able to use worn out "quilts" (e.g. tops & backings), worn out blankets, feed sacks, old sheets, used burlap -- anything that would trap layers of air. Why do you think we used to sleep under 9 or 10 quilts in the winter??!! Well, we had no central heating, for one thing, and "the girls'" bedroom was on the second floor and thus wasn't heated.
So, yes, you can make a quilt without batting. However, if I were doing a summer-weight quilt, I wouldn't use flannel for the back. That can get warm. What I now use, and I know this sounds a bit strange, but for a summer-weight quilt I have used diaper material. It's very thin, made of cotton, very breathable, very sturdy, and just enough to keep your quilt from being "see through" and give it a tiny bit of heft, but it doesn't add warmth. I'm talking about using a single layer here. It's cheap, and it's sold by the yard right off a bolt just like fabric. Google it on line. If you can't find it cheap, PM me and I'll give you my source. Don't even think you have to buy it from England, although they use a lot of it there because it's good stuff and cheap. (England may come up first on the web.) I know because I used to live there. It's a material that's seriously underused and poorly understood in the States.
So that's my suggestion! Good Luck to you!