The seats aren't narrower, just set much closer to the fuselage wall which in turn allows a wider aisle. I find them uncomfortable but Ok for a domestic hop.
Not that many EasyJet A319s now, think it has fallen to just 47 as new larger planes replace them
They are still receiving new A320neo and A321neo from a 2013 order, and at end of 2023 was confirmed 35 will be switched from A320neo to bigger A321neo
Subsequently another 157 planes (56 A320neo & 101 A321neo) have been ordered for delivery 2029-2033, with options for 100 extra planes.
So gradually upsizing the fleet
A319 have 156 seats
A320 have 180 or 186 seats
A320neo have 186 seats
A321neo have 235 seats
Having been on a sold out and full A321neo on a flight to Tenerife that got delayed by headwinds, and was about 5.5 hours onboard, they are cramped, and suffer from a semi-permanent queue in aisles at front and back for the limited toilets. They are too high density for longer flights.