If you shift slowly and your idle is not too high, there is no the need...I down shift all the time without double clutching... (just 3rd to 2nd) and with small tap on the accelerator, when I go around the corner, there is no grinding... City driving tends to make one get better at it... and does take time to get the feel for when to shift and how fast the engine needs to be.
That, said, I'd start out learning how to double clutch your car and over time, you'll likely learn to shift without it... that's what happened to me..