There are many options for shock-swapping and several options for lowering as well.
If you're going to a conventional, non-autoride setup, you'll want to bypass your autoride system so you don't have the "Service suspension" warning on your dash. This thread will tell you how:
http://www.tahoeyukonforum.com/threads/autoride-bypass.48518/
As I understand it, the autoride and conventional shocks are the same size, so you can bolt in whatever you want; autoride replacements from Arnott, OEM non-autoride struts, aftermarket struts, etc. If you liked the way your 07 Yukon rode, I would just buy some conventional OEM replacement struts.
Lowering the front:
Adjustable 1"-2": Belltech drop struts or McGaughy's coil relocators.
Non-adjustable 2": Belltech/McGaughy's spindles or lowering springs
3"+: Spindles and springs/struts combo
Lowering the rear:
Springs and possibly shock extenders, but I'm not sure exactly which springs are only a 2" drop. Belltech 5305s will get you a 3 or 4" drop, depending on whether you use the provided spacer or not.
2" front, 3" rear is the most common mild drop on these rigs. There should be tons of pictures and info on this forum about that setup.