Air carrier First Officer reported a fume/smoke event during cruise. After troubleshooting the flight crew returned to the departure airport where Maintenance met the flight and assigned an aircraft swap.

Narrative

[The] aircraft had two MEL's for pack 2 and the thrust reverser on engine 2. Push-back; take-off; climb and initial cruise occurred with no incident. About 15 minutes into cruise; we noticed the smell of smoke in the cockpit. I looked outside to see if we were flying through smoke; but saw none. The smoke got worse so we called the FA (Flight Attendant) and notified her. She reported smoke in the cabin behind row 18. We began running the arc for smoke/fumes and then executed the QRH (Quick Reference Handbook) [procedure]. My mask mic tested fine on the ground but was intermittent during flight. We notified ATC and returned to ZZZ1 as it was the closest and best suitable airport. We complied with the Quick Reference Checklist for smoke. Upon shutting off the fans and pack 1 per the Quick Reference Checklist; the smoke subsided. We continued to ZZZ1 and assessed for overweight landing. We executed the overweight landing with no issues. We did not deem it necessary to perform an evacuation and the [airport staff] escorted us to the gate. All passengers were deplaned with no incident. The GPU at the gate did not work so we kept [the] number 2 engine on. We did not start the APU to avoid any electrical load on the aircraft just in case it would cause another issue. The flight attendant was briefed according to the [company procedures] as required. Maintenance came on the plane and checked the plane saying the smoke was caused by the ACM (Air Cycle Machine) for pack 1. Flight was then delayed and a new plane was taken. Second flight completed with no issue. No medical issues for the passengers were reported. Quick Reference Checklist and Quick Reference Handbook were sufficient in assessing the problem and making necessary steps for a safe approach and landing. Perhaps use this situation for instruction to reinforce why we discuss duties [when there are issues] while briefing as well as why we discuss always checking for overweight landing if diverting in an unplanned manner.