Bcom/BSc - def the best option it will open lots of doors (if you choose majors wisely)
BSc (Adv) (USyd) - Still great but obviously limiting yourself to Science unlike the option of doing it with Bcom
BPsych (USyd) - Very niche and may push you into a corner you don't wanna be!
or BLaw/BSc (UTS) - eeeeeeeveryone does Law, do you wanna be a lawyer.
If you are interested in Psych, why not do BCom/BSc and do your science major in psychology? If you enjoy it so much you never want to do anything else =) you can transfer.
IMO unless you want to be a lawyer don't bother with BLaw. It wont open as many doors as you think if you don't want to be in Law. BCom and BSc on the other hand open lots of doors and many jobs overlap and make you uniquely qualified for them. Especially jobs for companies such as pharmaceuticals etc.