Glad you like your Sigma. The trigger is heavy, but ergonomics are great and you can't beat the price. I've been thinking about getting one again (used to have two, but traded them). I really don't need another 9mm (or .40), but the price plus the rebate is hard to pass up.
Anyway, at the time I had my Sigmas, I used Hoppe's Elite on them (both the cleaner and the oil). The stuff is expensive, but it (the cleaner) really works and virtually no odor and supposedly non-toxic. It even seems to remove some of the copper from inside the barrel. And it doesn't seem to hurt the plastic, either. I used the oil on them, too, and it did fine. Probably not as great a lubricant as some other stuff, but again low odor and non-toxic.
Since then I "discovered" Break-Free which I use on pretty much all my guns now. I'd imagine it would work fine on a Sigma, though I don't know what it might do to the plastic. I do know you should not spray the plastic with certain harsh solvent gun cleaners like Gun Scrubber or disk brake cleaner as they may "melt" or soften the plastic. I think Gun Scrubber does make a "plastic-safe" version, but I've never tried it.