JennaO,
I actually had that job for about 4 years. Our small design company designed/laid out book for the Meredith Corporation in Des Moines, Iowa. Until about 2+ years ago when their books devision was cut they published many DIY, gardening, cooking, children's, and other types of books. We did books for brands like The Home Depot and their 1-2-3 series, Stanley Tools, Better Homes and Gardens, and others. They relied pretty heavily on outsourcing the book layout and design to freelancers and small design companies like ours.
Even though you won't find and book design jobs at Meredith anymore, you'll probably find some possibilities with Wiley or Taunton Press. They still do quite a bit of book design and probably still don't do all of it in-house.
Something to do, is find a type of book that you would like to work on, and try to contact/get to know the author. Don't worry, most people that are authors for how-to books that I've know are pretty down to earth (unlike many famous novelists). They might be able to help you make a contact inside one of their publishers. Then it's just a matter of making a good sales pitch/proposal/bid and then delivering on the product.
Good luck,
Joel