F-150 to tow a light 5th - do I need HD cargo option?

I would definitely look at the new little dodge diesel or a 3/4 ton.

Be careful as even some 3/4 tons won't have enough payload. My '14 Ram 2500 loaded in crewcab form for example is just above 2300lbs. It does have sufficient axle ratings though.

The "little Dodge diesel" in the 1500 could pull it but you will be WAY over on payload etc. Worse than the F150. A crewcab 4x4 ecodiesel has less than 1000lbs payload.