M.H.
I recently finished reading Healthy Sleep Habits, Healthy Child, and i thought it was a useful book. One thing i liked about it is that the author offers solutions without ruling out your general approach - co-sleeping is alright in his book, as is complete cold-turkey CIO. He just mentioned different things you need to be prepared for with each method, and then its up to you to choose.
Ideas from the book that may help you:
1) scheduling can be your friend (although maybe not for another month) - maybe you need to set aside time for a nap, whether your baby seems to want one or not?
2) getting in tune with when your baby starts to get tired (earlier than you think) will help
3) your baby may need to sleep more during the day, not less - when kids get overtired they don't sleep well, so having only a short nap during the day may have made night time sleeping worse. Trying for two or three naps during the day may help.
4) self-soothing is good