It's almost always better to stay in 2nd if you can carry any speed at all through the turn.

Unless you're driving an old MGB or something, your transmission is fully synchronized, even first gear. FWIW, I've driven cars belonging to people who, like you, said "it's impossible to downshift this car into first gear". Never driven one yet that was a problem, you just have to give the throttle a good blip to match the revs.

A good way to practice this is to teach yourself to do a clutchless downshift. Usually a 4-to-3 or 3-to-2 is easiest. Not quite the same as grabbing first, but if you get good at that, you will have mastered the concept required to make a smooth downshift to first. Good luck!

(and if you need more info on how to do a clutchless downshift, lemme know)