Costanzo is an excellent book, but in total it is much briefer than Guyton (more clear and direct as well, but definitely briefer). If you are really gung ho about hemotology, I suggest getting a text just on that subject. Clinical Hematology and Fundamentals of Hemostasis by Harmening is pretty good. But I havn't checked out that many others yet for comparison. Unless you have some specific reason to get in depth about this subject before medical school, something like Guyton or Costanza should probably give you most of what you need to know for now (and for MS1 for that matter). Perhaps combined with relevant chapters from a good Histology text/atlas.
Oh yes, I almost forgot about Boron. Even heftier physiology text than Guyton and with a greater emphasis on molecular and physics topics from what I understand (I opted not to read this one, since Guyton and Costanzo had everything I needed).