Yes, I've read this too. Some editors and agents prefer two spaces after a full stop, colon, and exclamation mark (but not a comma or a semicolon), whereas others accept that most writers use one. My only advice would be to check with whomever you're sending your work off to. Personally I use one space, but that's just my preference.
Unless Teresa or someone else can give you more specific advice, since they're published? (Bear in mind not all countries have the same rules.)
Glad to help.