You are a Law graduate so, Law as optional subject is a natural choice. It has books and study-material in abundance. At the same time, we have some well-known coaching institutes as well impacting coaching for Law (optional subject).
In recent years, a lot of candidates have shown brilliant performance with Law as optional subject. Even, many candidates like Tapasya Raghav (AIR 78, CSE 2012), Nitika Pawar (AIR 18, CSE 2011), Ajay Katesaria (AIR 28, CSE 2011) and many more without having Law background have achieved high ranks with Law as optional subject.
Still, we suggest you to look at the syllabus and previous years’ question papers to understand the level and current trend and then make an informed choice.