Wait till the Zoji-La pass tunnel is complete. When we travelled in last June the work is going on. They work almost day and night and plan to finish ahead of time. This will cut down the time to Leh/Ladakh (currently more than 5 hours or more) to about 20 mins. This 5 hours is a low side estimate, each encounter with a flock of sheep/goat will take a minimum of 20 mins delay in overtaking them on the pass.
You don't need travel agents. Do on your own. We flew to Sri Nagar and started. There are so many travel operators and options when you get there.