Dont get upset .There are a variety of courses that can be done after commerce 12th.I will list some of the many...
its always safer to go for a Bachelor of Commerce (B.Com) degree at the least after 12th, and continue to M.Com if you're still interested.
the other choices are...
a) Charted Accountancy
b) Company Secretary
c) Chartered Financial Analyst
d) Actuarial Science (related to Insurance, Financial Analysis of companies etc.),
e) MBA (you have to write the CAT for that)
and other such courses etc.
You could also opt out of all this stuff and try for a marketing job or something directly (in which case you wont have luck anywhere if you haven't even done B.Com).
Oh yeah, there is also the choice of going to IIM's or XLRI's etc. where you'll really get a great boost to your commerce knowledge and fantastic job offers after passing through.
Yet another bonus which I forgot to mention is that you are not restricted to business related courses alone. You can even join computer-related courses offered by various institutions like NIIT, Arena etc. for further expanding your field and skills.
Also keep in mind that you can do multiple courses at once - for example, I'm doing B.Com, CA & GNIIT simultaneously.
By the way, I've probably not mentioned half the options you can choose from. I'm pretty sure there a lot more to Commerce than what the eye can directly see.
Now who said that the Science field has a lot more variety and scope than the Commerce field??