Touring colombia

I am planning on a trip to colombia some time next september or october.  I am primarily interested in Cartegena, Medellin and the carribean coast and all points in-between.  This trip would be for at least two weeks.  My primary reason for this trip is for a near future retirement place, but having a good time is a close second.  I am considering hiring a tour company for part of this trip, since i have taken trips in the past without one and ended up in a place where i know little about with no way of getting around, so i want to avoid this problem on this trip.  I realize that it would make sense to fly from Medellin to Cartegena, but besides that, i would need some guidance.  Can anybody recommend a tour company that could help me get the most out of this trip.  thanks in advance.