I want to upgrade to a car that offers noticeably better ride comfort and suspension refinement while keeping the same exterior dimensions as my current car.

The Citroen C3 has a very good ride, and it is within the dimensions of your current car. However, it would not feel like an upgrade, more a lateral move at best, so take a good look at it and see how you think about the car. You can also look at the Tata Altroz, which also offers a very good ride. 

If you want to stick with an SUV body style, then have a look at the new Maruti Suzuki Brezza. The car looks and feels quite different from your older model, both inside and out. The ride quality has also improved. It is soft and pliant at low speeds. 

Though at higher speeds over crests and undulations, there will be some pitch and lift. If your running is mostly in the city, this would not be a problem and assuming you are happy with the Maruti Suzuki car experience, the new Brezza would do well.