Your interface is always super personal.
This video I made a while back sums up pretty much everything that I think is required to have as a healer
The important takeaways are: You need boss timers, and raid frames that you can use mouseover macros on and see debuffs effectively. There is no “best” addon for these or the rest of your UI - it’s just personal preference.
There are a few good macros to have as a Discipline priest.
First off, making nochanneling macros to avoid clipping your Penance is a relatively big deal, since doing it manually you either risk clipping your Penance or you waste a little bit of time at the end of each one, adding up to several casts in total over an encounter.
A standard nochanneling macro with Smite would look like this:
/cast [nochanneling] Smite
Angelic Feather Macro
Another very useful macro is a macro that has been mentioned before, one that automatically places an Angelic Feather underneath your feet, instead of having to manually put it down in front of you every time.
#showtooltip Angelic Feather
/cast [@player] Angelic Feather
Power Word: Barrier Macro
If you want to try and be fast and clutch with Power Word: Barrier, you can use an @cursor modifier to make it instantly used on your cursor placement rather than going the extra step to click the spell. This can be done with any targeted AoE spell, like Mass Dispel.
#showtooltip Power Word: Barrier
/cast [@cursor] Power Word: Barrier