http://www.fpsc.gov.pk/icms/admin/fi...us-updated.pdf
Consult the above mentioned old syllabus of CSS, it is same as of PMS. It contains all the suggested readings. Now you have to act smartly as it contains a lot of readings and it can take years to go through all. Just consult the ones which cover all the topics mentioned in the syllabus. If you're 27 or below try to consult books which can help you in CSS as well.

For instance English composition remains the same in old and new syllabus so just consult two books. Similarly, Pakistan Affairs and Current Affairs are almost same so along with newspapers and periodicals two or three books of each subject will do the work. Current Affairs wont be done alone by Dawn, you need to consult some readings as well.

Coming to optional subjects, lets say Islamic History or Indo-Pak one is going with. The History of Arabs by Philip K. Hitti for paper 1 and Dozy. R for paper 2 are enough and cover every content. Whereas, for Indo-Pak, A Short History of Pakistan by I.H. Qureshi, Struggle for Pakistan by I.H. Qureshi, The Idea of Pakistan by Stephen.P. Cohen and the Future of Pakistan by Stephen.p.Cohen. If you include the book by Hamid Khan as well then you cover all of the contents of paper 1 & 2. Value addition= Pakistan Affairs gets done with it too.

Plus If you have money and can buy 4 or 5 books of each subject that would be amazing. Then you just need to look the contents, refer to the parts in those books and take your own notes. Not only it would be a great research and splendid preparation, but most importantly it will reward you. Though hectic this exercise will be beneficial for CSS as well.

However, If you are nearing the age bar, then you should consult these books by just tweaking your strategy a bit considering the paucity of time and age factor at hand, just pick your contents rather than thoroughly reading.