I have this one:
Bergan Comfort Carrier - Carriers - Cat - PetSmart
I used the small one until Duke turned 2 years old. He's about 7-8lbs now.
I have the black one. It's not fancy, I use it to travel on the train and car and around town. I like it.
The only thing it doesn't have is the hook to hook him in while he's in the bag. I don't need it because Duke is not a dog that I can allow him to peak his head out while in the bag so this works for me.
I hope this helps. These bags only come in Small or Large.
Good luck.
Tam and Duke