If you can read Tamil, the definitive edition is by U.V. Swaminatha Iyer. While this is the Tamil original, it is the verified source text.

For the complete ancient epic (Mahapurana) translated into Malayalam, you may need to look at digital libraries:

In the opening verses, Manikkavasagar presents a paradox. A "Purana" implies a history—something that happened in the past. But God (Shiva) is timeless, formless, and eternal. How can there be a history of the Timeless?

Sivapuranam Malayalam Pdf Verified