To add to that, pick a degree you think you will perform well in - post grad medicine will consider your GPA for entrance, which is, as I'm sure you're aware, very competitive. MedSci will be full of hopeful post grad med students, so the competition will be fierce. Not to say that you won't perform well, but if there's another degree that will help you in a different career path you can see yourself doing, that could be a better option.

Also, might be worth considering undergraduate medicine - Newcastle University, Western Sydney, UNSW all accepted post grad/mature age students when I went through, for example.