Well, if you are choosing between actuarial science and computer science/software, why not do both in a double degree!
You can pick an actuarial studies major in the Bachelor of Commerce, Commerce Specialist or Science. With Commerce Specialist, you'll be able to jump straight into actuarial studies, while in standard Commerce, you'll have to undertake about 6 required core units in different areas (Business Law, marketing, management, etc.) Meanwhile in Science, you'll be able to gain more breadth of study in other science areas before majoring financial/insurance/statistical mathematics. Just a note here, to gain accreditation as an Actuary, you will have to complete/pass certain exams with the Actuaries Institute, but depending on your degree/which units you pick, you'll be exempt from some of them. So it might be worth going to Monash open day (which is quite soon I believe!) and have a talk with people from both commerce and science.
You can then combine that with a study in software/computer science in a double degree with Bachelor of Computer Science, Engineering (software) or Science. I'm not too knowledgeable in this area, but I believe Computer Science deals with both software/hardware, while software engineering deals mainly with software. If you choose to go through a Bachelor of Science instead, you'll be able to receive a broader science study (like above) before majoring in computational studies. This is my opinion only (and I could be very wrong), but I think that in the end, how you end up with a computer studies/software degree won't make a massive difference to an employer, provided you can still solve their problems

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EDIT: Apparently there's also a Bachelor of IT. Like I said, plenty of options

So possible degrees include:
BCom/BCompSci
BCom/BSc
BEng/BCom
BEng/BComSpec
BEng/BSci
BComSpec/BSci
BComSpec/BSci
There's a few combinations I haven't listed, but hopefully this will get you started

Ultimately, you decision will most likely lie in whether you want a broader focus, or want to go straight into a specific area. And if you get into a double degree and end up not liking one side, then there's always opportunity to drop a degree and continue with a single degree. But like I said, attending open day might be worth going to, to have a look at the different ways you can study software and/or actuarial studies/statistics, and which one is likely to suit you.
I can't say too much on the job prospect side of things, but I'm sure having both the technical/logical side of Computer Science/software combined with the business-oriented side of Commerce would give you an advantage of sorts

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Hope this helps somewhat
