- Forensic science
https://en.wikipedia.org/wiki/CSI_effectAs someone who's used a lot of the techniques and things you see on CSI, its nothing like the show. It honestly isn't. It's slow, boring and it very rarely all fits together perfectly in a puzzle like you think. There's a lot of paper work and theres no orchestra to follow you around playing dramatic music while you get your science' on. It becomes old very quickly. Most of the time in this situation you'd just be writing up the results, you might not even know all the details. Someone else pieces together all those things.
I'm not going to go through the rest in detail. Law? Sure if you like pouring over thousands upon thousands of words of boring laws. It not like you're in law and order. It's hard work and the hours are long. It seems like you're leaning more towards the criminal side of things. Sometimes you have to cut deals, its part of the job. It takes a lot out of a person.
Criminology isn't as interesting as you think, theres a lot of boring theory and papers to read...good luck finding a job in it too. Same for pysch, theres way too many graduates out there. Philosophy is only good if you want to teach it/become an academic, indeed IF you can become an academic. I think its a bit less learning and a bit more skill than some of the other areas you might find within the academic community, it certainly helps if you have a flair for it. If you don't, it might be hard to even make it through your undergraduate life. It seems interesting to people on the outside but once you actually have to do work and write an essay on it, a lot of people rapidly change their mind. If you're only getting a 30 in it i'm not sure if you posses that burning passion a lot of other philosophers in the field have. I'm not putting you down nor have i done VCE philosophy (have done uni philosophy though) but its a bit of a strech to expect that to magically change. These are signs and you should maybe take these into consideration. If you'll always love something later or get better at it later that wont take you anywhere good...really..if not now, then when?
Not to be the bearer of bad news or anything. If you actually like any of these fields then go for it but first actually know what you're getting yourself into...knows the reality of it rather than some other picture you have.
ASIO and ASIS are probably nothing like you picture. Most of your time is spent in meetings (as a government run bureaucracy surprise surprise!) or on a desk analysing things and writing up reports. It's certainly nothing like mission impossible, especially for Australians. There aren't all that many openings for forensic scientists (as far as i know) nor can you just "join" as a detective. You need to work your way up.
It's nice to have someone else make your choices for you but at the end of the day you need to look into these things at a much deeper level than you already have. It's alright to make mistakes in uni...transfer...change your degree but its still essential to have some kind of direction sooner or later. Only you can answer many of these questions yourself.
I think a general degree (Eg. BA or Bsc) will be a lot better for you and give you much more wiggle room than a degree with a more narrow scope like "forensic science" .