Dismiss my natural bias against all things left-handed...The only thing I have ever been able to do with my left hand is punch.
I would suggest that you learn to box right-handed. Your front hand- in this case your left- does 80% of the offensive work. and having a strong natural left hand can only be an advantage. In the old days, when guys knew how to fight, most guys relied on their left hook. The right hand is so much harder to land, when fighting guys that can fight, and you still need the hook to finish the job.
The biggest thing, in my mind, is what it does to your boxing education. It skews the game and you will find that there are so very very very few trainers out there that can actually and effectively train a southpaw. Its not the same thing and i don't care what may be said- years ago there were guys that could really educate a leftie but that no longer exists, at least in my view.