Hester Browne was who I was going to recommend first, so I'm glad you've found her! Which one are you reading?

I haven't read all of these, so I can't totally vouch for content, but as far as I know they seem like possibly good fits -

Meg Cabot's adult novels

Jane Green

I just got one called A Hopeless Romantic by Harriet Evans that's supposed to be like Hester Browne, but I haven't gotten to read it yet.

If you do feel like young adult fic at any point, I've really enjoyed Maureen Johnson's books - they're funny, not over the top romance, and typically very real-worldish. The Name of the Star series incorporates a mystery, too.