The Writers Market and Writers Digest both say to keep it to one page double spaced. I found it hard to say what I wanted to say, but after a few tries I did it and liked it.
I've never heard double-spaced for a query either, and I can't imagine being able to fit much of anything in that space after your contact details and you've had a chance to tell the agent where you found her/his name (as a way to personalize and show you've done some homework), and ended with the usual "happy to send more...look forward to hearing from you...thank you for your consideration..."
However, I believe one page single-spaced is sparse enough to satisfy an agent and sufficient to get the information you need in the query.
Start with "the hook", lead into what it's about, why it's different or compelling.
Include a paragraph on your specialized expertise or access to different types of stories and certainly mention your publishing history, which would give credence to your writing ability.
Then post your query in Share Your Work for a critique. People are honest and helpful.
I hate to rain on your parade, but if the only market you feel you have for your book is church groups and ladies groups, this is not going to impress a potential agent. I see that you actually don't say that the query is for an agent, but my own recommendation is to concentrate on small regional publishers, unless you have some sensational, personally witnessed stories on highly visible public figures - or you are one!
Best of luck.
