As a disclaimer: I don't really know very much about these kinds of degrees. But anyway...
Doing health science at latrobe and then transfering after a year, especially if the subjects are all the same, is a good option. Usually to transfer you need about a distinction average, which, if you enjoy what you're doing, wouldn't be too difficult.
I don't think there really are any 'secure' pathways, because there's always the chance that you'll be denied to get into the course you want, but within-uni transfers are usually more 'secure' than transferring to another uni (although transferring from melbourne to latrobe would be fairly easy, I think).
Completing a science degree and then doing postgrad physio is also a good option. A general science degree from Melbourne is well regarded throughout the country and you should be able to go somewhere with it. It's also a good back up to have if you don't get into physiotherapy.
Your ENTER isn't far off from the Chales Sturt cut-off, so there's still probably some hope of getting into that course as well.
This is a choice you'll have to make yourself, but I think it depends on when you want to start studying physiotherapy. If you're fine about waiting to postgrad, then maybe going to Melbourne uni is a good idea, if you'd like to get into it straight away, then health science is the better option. Either way, you're going to have to work quite hard to get good results to make it easier on yourself to get into physiotherapy, but it's not as though you go to uni to do badly anyway.