CRJ-200 First Officer reported due to a differed and failed second pressurization pack resulted in a return to departure airport.

Narrative

Aircraft X scheduled ZZZ to ZZZ1 departed [Runway] XXR and conducted a normal takeoff. Upon following the guidance of the MEL for single pack differed bleeds transfer; and after reducing N1 to 60% for the swap; a Left Pack HI Press Caution message on EICAS (Engine Indicating and Crew Alerting System) and an associates Fault light on the Left Pack overhead panel appeared. The Captain (Pilot Monitoring) began the QRH for the associated message. The QRH procedure assumes the other Pack is operative; which for our plane was previously deferred; and as a result the aircraft was climbing out on the departure procedure in an unpressurized manner. The decision was to limit our final climb to 10;000 feet while working the problem. A Cabin Altitude Warning message appeared after the Left Pack HI Press QRH was completed. After completing all associated QRH and directed CFM procedures; it was determined that we would have to remain unpressurized and below an altitude that would allow for us to complete the flight segment to ZZZ1. Our fuel numbers suggested the best course of action was to return to ZZZ. After making the decision to return to ZZZ; we notified Dispatch and Maintenance Control via ACARS of the issue and plan to return to ZZZ. Our FA (Flight Attendant) was notified via his handset and briefed.The return flight required us to burn a little fuel to land under maximum landing weight; so we continued to maintain an altitude of 10;000 ft. to expedite the burn. The cabin temp reached as high as 35 Celsius during our flight. We landed back in ZZZ on Runway XXL and taxied to the gate without further incident.Deferred packs for ZZZ would be preferably fixed instead of deferred. Given the single pack taxi operations in summer weather; if a fix is not possible; maybe positioning the aircraft to fly northern rather than southern routes would be more comfortable for passengers.