I've never used a travel agency or booking service. It's never seemed necessary to me, and it would limit my choices.
What is the "Final Bit" you're lacking?
Do you have flights? If so where are you flying in to?
Rental car, public transfer, or transfer company?
Then decide based on where you are flying in to and how you want to travel where you want to go (your skiing preference also obviously influences this).
You mention Austria, Most resorts have in addition to an online booking tool an additional service by which you write the tourist office the basic parameters of where you want to stay and they forward that on to hotels/condos. Owners then have 48 hours to send you offers. You can then choose from those offers.
That's how I do it. Maybe there is some great added service from a travel agency, but I don't see it.