AFAIK there is no shuttle option that doesn't have you changing vehicles at a bus station - big bus from airport to station, change to small bus from station to hotel, reverse for the return to the airport. I know both Greyline and Flybus do this.
In case it helps, my experience has been that it is a very easy transfer and they walk you through it pretty well.
If you want truly direct with no change in vehicle I think your only option is a taxi.
If someone knows a shuttle that does direct, I'm sure they'll be along to supplement my info!