Considering you already own a Mahindra car, we would have suggested the Mahindra 3XO. It has a very smooth 6-speed torque converter automatic, but fuel efficiency from this gearbox and turbo-petrol combination is not the best.
Based on your requirements and considering that you already have a large SUV and need this car purely for city commuting, we would suggest the Hyundai i20, the Sportz (O) IVT variant. It is powered by a refined 1.2-litre naturally aspirated petrol engine paired with a smooth CVT automatic.
The compact size, light controls and smooth gearbox make this Hyundai car extremely easy to live with in urban conditions. The car is also spacious, feels premium on the inside, and has a large boot. Fuel efficiency will also be noticeably better compared to turbo-petrol engines.