For giving upsc exam you just need a graduate degree therefore you can surely opt for doing bcom hons.As far as MBA is concerned it is a post graduate program doing it or not won't effect your eligibility criterion but it may hamper your time in the preparation of civil services.

Dear candidate,

The Civil Services Examination (CSE) is a nationwide competitive examination in India conducted by the Union Public Service Commission for recruitment to various Civil Services of the Government of India , including the Indian Administrative Service (IAS), Indian Foreign Service (IFS), Indian Police Service (IPS) among others. [1] It is conducted in three phases - a preliminary examination consisting of two objective-type papers (General Studies Paper I and General Studies Paper II also popularly known as Civil Service Aptitude Test or CSAT), and a main examination consisting of nine papers of conventional (essay) type, followed by a personality test (interview).

Keeping this in mind, you may surely opt for B.Com hons, and simulataneously prepare for UPSC. MBA is a post graduation course which you may opt for after completion of your bachelors degree.

All the best!