I know this is an older post, but I thought I'd answer in case you haven't received any recommendations so far. Sharon Kay Penman writes books in the Katherine vein. Her Sunne in Splendor is my favorite book, bar none. Some other authors to look at- Anne Easter Smith, Edith Pargeter, Elizabeth Chatwick, Parya Primar, C.W. Gortner, Ellis Peters (more mystery, but very good historical fiction as well), Mary Stewart, Sandra Worth, Susan Higgenbotham, Rosemary Jarman; Good King Harry by Denise Giardina, etc. That's all I can think of for the moment- hope it helps!