It sounds like you found some excellent sources!
I would like to contribute my current favorites. Links to Amazon - most of these are available on Kindle if you're into that.
The Upanishads from Halcyon Classics
http://www.amazon.com/The-Upanishads...2795057&sr=8-1
The Upanishads by Eknath Easwaran
http://www.amazon.com/Upanishads-Cla...2795010&sr=8-2
Eknath Easwaran also provides prologues to each Upanishad that can help solidify understanding. I really enjoy that one.
Journey from Many to One Swami Bhaksarananda
http://www.amazon.com/Journey-Many-E...2794988&sr=8-4
I would definitely suggest reading this after another source.
Bookmarks