The order I do these in for a desk back

Thoracic first, always. Skip straight to hip flexors and you're just stretching around the actual problem. (modify as needed)

01
Cat-Cow
Wakes up the spine before anything else. 10 slow reps, not fast ones.
02
Open Book Stretch
03
Foam Roller Thoracic Extension
04
Prone Press-Up
Push up from the floor, hips stay down. Undoes an hour of slouching in about ninety seconds.
05
Thread the Needle
06
Doorway Pec Stretch
Your shoulders round forward because your chest is short, not because your back is weak.
07
Wall Slides
08
90/90 Hip Stretch
09
Couch Stretch
The one everyone skips because it's uncomfortable in year one. By year three it's fine.
10
Pigeon Pose
Breathe first, don't force the front leg flat.
11
Glute Bridge
12
Deep Squat Hold
Two minutes if you can get there. Most desk backs can't yet, that's the point of the rest of this list.