Commas almost seem to have become a personal choice. Even good writers do what’s more comfortable for them and some don’t bother much with the little curly thing. It’s probably a question of habit, too. And yet! How many sentences have I not misread due to the lack of commas!
I would normally put a comma after ‘so’ when it has the meaning of ‘therefore’. The lack of one in your sentence doesn’t cause confusion, though.