"He always finds things o'er which to mull" - This isn't too big an issue, but it is too many syllables. Something like, "He finds things over which to mull" would be smoother.
"So Sam went directly off to his mother" - "directly off" isn't quite right. You could take out off. Or, even better, you could say, "So Sam went directly to his mom."
"And she looked right at him and said" - I would take out right.
"So Sam went directly off to his lair" - directly doesn't feel right here. Also, "directly off" echoes from a few lines above.
"He made sure he remembered his good mother's words" - This is too many syllables again. Personally, I would change it to, "He called to mind his mother's words."