CE-compliant Schuko mains power switch: do I need to switch both poles?
Assuming that EN60950 applies to your power meter, in a case where the mains plug is reversible then EN60950 requires that a disconnect device "shall disconnect both poles simultaneously" (section 3.4.6). However, pulling the power meter out of the mains socket will disconnect both poles simultaneously and so it is quite valid to consider this to be a disconnect device. Most domestic electrical equipment sold in the EU has a mains switch which only switches one pole of the mains supply and relies on the mains plug as the EN60950 disconnect device.

For CE compliance your relay only needs to switch one pole.