Interesting, my son is left-handed too. I have wondered if it makes a difference.
It does. Writing is naturally harder for left-handed children, especially as they will be being taught (usually) by right-handers. Letter formation assumes right-handedness.
Left-handers often struggle as they cannot see their work as they are writing, and they often smudge as they move their hand along, so to combat this they end up holding their hand higher above the paper and at an "incorrect" angle, called "crabclaw" writing. This is an incredibly uncomfortable way to write
Furthermore they have to "push" the pencil/pen away from their bodies as they write, unlike right-handers where it more "pulling" it towards themself.
When left-handers attempt to write like a right-hander, the natural motion of their wrist can cause the writing to slant the "wrong" way, which makes forming letters "correctly" harder. This is "backhand" writing.
Often, the solution is to manipulate the angle of the paper, rather than their wrists!
You can find a lot online about the challenged of handwriting for left-handed children.
You might want to find some resources for left-handed writing online and see if you can print anything out that may help.