Try Auschwitz and Wieliczka Salt Mine, now available as 1 day tour. More to see in limited time, for great price. Check www.YourKrakowTours.com for price.
For Old Town, Kazimierz and Podgórze with Schindler's factory sightseeing I suggest using electric cart Melex (golf cart) with audio system in 2 hours you'll see most important places and save your feet, www.abcitytour.pl is the company I used when my parents came to visit.
Best regards and have a nice stay in Krakow