Then perhaps you should approach the story differently. Your original backstory is a good one, but here's another, one the SW story itself facilitates for:
You are a Sith, but you are not evil. Upon beginning your training you quickly became disenchanted with the Sith ways (as you as a person have). But instead of defecting from the Empire which you hold in such high esteem, you attempt to reform it from the inside, by rising in power and influence and making yourself an example to others. It is not always necessarily to slaughter innocents, torture, back stab and betray, your enemies can be used, converted to the other side. Have you played KOTOR 2? If so adopt Kreia's policy 'do not adhere to a single idea' adapt to the situation as you see fit and do what you think is right. I'm sure you'll end up with a very interesting character who if rolled male, gives a lot of options for Vette and LS Jaesa. (LS Jaesa will be a boon to developing your character and emphasising on this stand point, as her philosophy would mimic yours.)
SI can be done in a similar way, though I'd suggest SW first. Just remember, playing LS Empire works a lot better than playing DS Republic, you'll soon find that. LS DS choices are there for a reason, so you can develop your own personal character, and that's whoever you want it to be.
That's exactly the way i play my Warrior! :-D