a staff is 2 handed (assuming it is AT THE LEAST a quarterstaff sized weapon) and would then require two hands to use, but casting a spell should only require one hand....
if you really wanna make things cool, create a buckler than can "hold" spell components (like a spell storing item [which would be cool on a buckler] or a bracer of storing type thingy)
then its just looking like a bamf and casting spells ALL WHILE WEARING A SHIELD
and bucklers are worn on the forearm, switching a weapon should be a SWIFT action rather than a free action, and depending on the weapon, should provoke AoP, if its a light weapon then no AoP, if its larger than that, give them an AoP
the only reason I say that is because I once played a Paladin Sorcerer who used a Greatsword...so switching to cast a spell would provok an AoP, let alone casting the spell, needless to say he became a Cast first, Charge and Smite second, ask questions later kinda character....until he met storm giant who liked to bull rush people off cliffs...
