Hope this doesn't come off as spammy, but if you're looking to book a hotel room the last minute there is a new hotel that is just having their grand opening.
Hotel Clariana on the corner of 3rd St and Santa Clara in downtown is finally open. If you're still looking for a hotel downtown that could be an option. It is a walk though, as opposed to a hotel like the Marriot or Fairmont that are right by the convention center.
http://www.hotelclariana.com
https://www.facebook.com/hotelclariana/
I haven't stayed there or heard anything about it since it is brand new as a hotel (the building was an office building in its past life). If anyone does stay there do let me know how it is.