If u are doing self-study do P C Tulsian for concepts and solve PM 2-3 times. U can easily score 75+. Also, in cover theory well as they come for 32 marks, are easing and attempting them will help u a lot in completing the paper. For costing theory PM is enough. But, for FM u have to complete entire theory as its syllabus is small.
Its my personal experience. For FM I had taken Mohit Jain classes. He provides a theory book of about 40 pages and all theory was from it only.