Comfort probably comes mostly from having a good pair of bike shorts, and a seat that agrees with your anatomy.
As far a fit goes, most bike frames come in different sizes, and handlbars can be raised, seats can be raised and adjusted, so that things fit.
For fully supported touring, you will not be carrying much. First, make a basic decision on what type of bike you want to buy: Road, touring, or hybred. Then look at the Trek or Cannondale line and figure out how much you want to spend. They have bikes in a wide range of prices. Obviously, if you spend more, you will get a better quality components. But, it's cerainly possible to bike a long long ways without major problems with a modest priced bike. I know, because that's what I have.