Glad you enjoyed your lesson! :) And even more glad you fell in love with a Thoroughbred.. they're amazing horses, aren't they? And if you get into jumping, they tend to be pretty awesome at that too!
For boots, I always wear tall boots or paddock boots with half chaps. I like having something covering my entire calf for two reasons: 1. Stirrup leathers won't pinch, and 2. God forbid you hurt your leg, there is more stabilization (been there, done that unfortunately).
Good luck getting back into riding! I rode for ten years as a child, but had to quit when I went to college. I finally got back into it when I was 26. Six months after starting lessons, I was leasing... next thing my poor husband knew, we added four hooves and a tail to the family. And he thought I would just be taking a lesson once a week. ;)