The OEM case is very functional but it is quite bulky.
Based on your needs I'd go with th Fortte STi.
It meets all your requirements.
Slim - yes (you might consider the fixed clip option. I haven't tried it personally but out of the six clip options it looks like the slimmest.
Style - yes. You can choose from a variety of colors and even special order all leather (no elastic sides) if you so desire.
Sleeper Magnet - yes. It has one and works perfectly.
If you don't like the idea of having a topless case than take everything I said above and apply it to the Fortte Vertical Pouch. It's not as bulky as the OEM case. www.fortte.com