Some single width RCBOs are single pole only. Would you recommend a RCBO
that disconnects the neutral as well?

A DP is nice, as it can act as an isolator for the circuit. Particularly
useful for maintainance, or if a neutral-earth short has caused the trip on
that circuit (will prevent other RCBOs tripping too). However, there is no
requirement, AIUI. After all, an MCB is single pole.

Christian.