Distilling it down to the episodes I usually go for when I just want to have some Star Trek on:
Balance of Terror
That Which Survives
The Savage Curtain
Samaritan Snare
Peak Performance
Yesterday's Enterprise
Cause and Effect
All Good Things
Whispers
Civil Defense
The Ascent
Take Me Out to the Holosuite
"The Ascent" is my favorite comfort episode of DS9 for sure.