You might want to try Green Nature Books http://www.greennaturebooks.com/
His books are more on his adventure of keeping Tortoises and some practical hints about what he and some of the successful tortoises keepers do to keep their pets healthy and happy. The book is self published (Read photo copy, stapled and bound) but it is an easy read and at times will make you laugh, smile and give you a feeling of dayjavu (he sometimes repeats stuff in his book).
You can also try Carapace Press (Tortoise Trust) www.vidi-herp.com. they offer a few books on different types of tortoises. They are fairly thin and much harder to read than the adventures in Richard's books (Above).
Also note Red foots and Yellow foots are very different to keep - Yellow foots require a much higher humidity, eat a different diet and have a different UVB requirement.
None of these books go into diseases or parasites in much detail. Something you will want to know about if you get an imported Tortoise.
Good luck in locating the a good book on Torts - I know it is very hard to find all the info you want in one book. I have lots of reptile books with a few pages on tortoise and err lets say my girlfriend has banned me from buying more.