If the winter is mild then fleas are a big problem around here. My cat gets treated every fall, and personally I suspect that he gets the fleas from the kids hanging out outside or being around other animals (or in the case of our one major infestation, from my MIL's dog--sigh)
We do advantage too, but only for a few months after an infestation, as it's pretty expensive.
This year hasn't been too much of a problem!
One thing you might look into, is to pick up a few 'capstar' tablets from your vet. Capstar essentially kills all the biting fleas on the cat. We had a major infestation a few years ago, and had to use the capstar daily for a week plus advantage for a few months. I also used a spray (it wasn't insecticide, but it wasn't organic either) under the bed where Oliver spends most of the day snoozing. If you end up having to use capstar, it does involve pilling the cat (which can be a major pain).
I found capstar/advantage to be less intrusive than flea baths (or even just advantage) but to be honest if you've got a big infestation then advantage is not going to be enough, you probably need to do capstar or something like the baths to kill the adults.
If you're worried about the yard, I believe that if you apply predatory nematodes they also will eat flea eggs or larvae, and you should be able to get those from an organic garden story (might want to make sure of what kind to get). Unfortuantely, that has to be a seasonal thing, it won't solve an acute problem. But might be worth looking into if you think they're being tracked in from the outside environment.
I can look up the spray I used if you want. I never bombed the house, and the spray seemed pretty effective. Also, fleas can be dormant in your house for a really long time. My MIL's dog picked up its infestation when they ripped up a bunch of carpet and were redoing the inside of their house, fleas had never been a problem before. Those little buggers are a real PITA, especially if you've got family members that are sensitive/attractive to fleas (they love DD and me).