You are thinking of the word "business"; which unfortunately at melbourne is very different from. An eco finance major at melbourne will give you precious little knowledge of how a business is run and how to adequately deal with clients/customers. It is definitely the 2 most maths heavy majors in a b.comm (asides from actuary - which i would class more as a maths degree rather than a commerce degree anyway), so you will be dealing progressively with more and more maths and "probability/statistics" as you get into 2nd and 3rd year.
Economics at higher levels requires quite a bit of calculus and algebraic manipulation (since the whole concept of opportunity cost stems from this anyway). Finance may be mathematically harder or easier depending on how you view maths because it involves a lot of algebra and equation manipulation. Meaning a lot of inserting numbers in formulas given to you, but having to understand what goes where (a lot of people can have trouble visualising financial models).
If you want a more "management/business" style majors, I would recommend accounting. It is very different from most peoples view of what accounting is (incl. myself before actually doing it myself) - a lot the accounting subjects are essentially management subject with a bit of adding/subtracting involved. Compliment this with either an actual management major or a marketing major and it would be what I think you are looking for.
Also accounting, management and marketing would be the least maths heavy majors available. (melbourne does require all their students to take up QM1 in 1st year - but thats the most maths you will need to see for the degree.
Personally, I think you wont learn anything that relates to "how" a business is run, at uni. Your best bet is to actually take up employment, if you want to understand the workings of a business.