Thank you for your suggestions. It sounds really natural to correct the DA since you don't want to go below the actual published minimum altitude, so I see what you guys are doing. However, in my company's latest documentation (August 2018) I can read the following statement:
"As per EASA regulation temperature corrections for the FAF and DA are no longer allowed when flying RNP approaches down to VNAV minima."
Could this mean that the published FAF and DA are determined using the minimum temperature for the procedure. Then no correction would be necessary, even if you're below zero (but not exceeding -20 in this case).
For the second question, we operate the 737 so it's uncompensated Baro-VNAV. Means we can fly the approach down to the minimum temperature, like you said.
Thanks again!