Stroller for a Cavalier King Charles Spaniel?

I'm looking for a stroller or rolling bag for my dog. My intent is to use it in the airport. I currently use a Sturdibag, but at 19lbs, I'd like wheels. A pull bag concerns me because I'm affraid people won't know it's a dog and be careful. Ideally, the bag (attached to a stroller or simply with wheels) actually fits under the seat on the plane so I don't have to change bags.