Another lefty, here.
Just flown an RV7 (essential maintenance flight) from the left seat, left hand on the stick and right hand on the centre throttle. 1st time landing this particular model, not an issue. I initially learned on a Rallye with 2 throttles so flew right hand stick, then Cessnas/Pipers with left hand on column and right hand on throttle. Then instructor course in the right seat, flying right hand again. Never had a problem switching one hand or the other, or one side of the cockpit or the other. I really can't write with my right hand, though.
Now, the OP was asking about writing and there's some good advice above about trimming. Time without number I've had students (right-handed ones, anyway), grip the control column on a PA28, then when they want to write, the pen hand and the left hand on the column come down together, leading to a nice spiral dive to the left, which they don't notice with head-in, writing. I teach them to LET GO, write what you need, then glance up between words. If a wing is slightly low, make a correction with rudder. Thus, it won't matter what hand you use for flying or writing. But if you're not trimmed...
I've read somewhere that about 10% of the general population is left-handed but over 30% of pilots and an even higher proportion of astronauts are leftys. Apparently, we have better spatial coordination. So, what is it about flying that attracts left-handers in the first place?
There's a shop for leftys in San Fransisco but I found most of the gadgets like left-handed scissors etc a bit gimmicky when I visited. It's a right-handed World and of course we're good at accommodating the unthinking right-handed lot.
TOO