Sorry to say you, but you can not do IPS after passing 12th with commerce, it is mandatory to hold a graduation degree to apply for this examination. so you should wait till the completion of your graduation. But you can start your preparation while studying 12th.

Other details of IPS examination
Nationality:
A citizen of India, or
A subject of Nepal, or
A subject of Bhutan, or
A Tibetan refugee who came over to India before 1st January, 1962 with the intention of permanently settling in India, or
A person of Indian origin who has migrated from Pakistan, Burma, Sri Lanka, East African countries of Kenya, Uganda, the United Republic of Tanzania, Zambia, Malawi, Zaire, Ethiopia and Vietnam with the intention of permanently settling in India.

Required qualification:
The applicant should hold a graduation degree of any of Universities incorporated by an Act of the Central or State Legislature in India

IPS exam syllabus

Paper I :- General Studies covering Current affairs, History of India, Geography of India and the world, Indian polity and Governance, Economic and social development, Environmental issues,General Science

Paper II :- Aptitude test comprising Comprehension, Interpersonal skills, Logical reasoning and analytical ability, Decision making and problem solving, General mental ability, Basic numeracy and English Language Comprehension skills

Paper III :- English Language paper. This paper would be of Matriculation standard and qualifying in nature only. Its marks will not be counted for preparation of merit ranking.

Paper IV :- Essay paper. It will comprise two essays, one on security aspect and the other on various developmental aspect of the society.

Paper V:- General Studies paper covering various aspects like Elementary Principles of Public Law, State Policy, Fundamental Rights, Human Rights, Disaster Management, National Security etc.

Part B PAPERS OF DESCRIPTIVE TYPE

Paper III : English (200 marks / 3 hours duration) :- This will be a qualifying test only of Matriculation or equivalent standard. The aim of the paper is to test the candidate’s ability to read and understand serious discursive prose, and to express his ideas clearly and correctly, in English. The pattern of questions would be broadly as follows (indicative only) :—
Comprehension of given passages;
Precis Writing;
Usage and Vocabulary;
Paragraphs writing;