Your limiting factors are rear axle capacity and cargo capacity. For a good comfort factor, you will probably need to look for a HD version of a 1/2 ton or a 3/4 ton.
1/2 ton HD versions generally have beefed up suspensions, axles and heavier load rating tires, vs the non-HD versions. Be careful to get the exact correct numbers, don't guess.
Engine power is not your limiting factor in most 1/2 tons. The Ford Ecoboost is a towing beast, for one option. Gets upper teens mpg as a daily driver, or better, depending on driving habits.