Body length should not have much impact on comfort outside the smallest size hammocks. It is unusual for the body length of hammocks to be less than six feet and most are at least seven feet. Hammocks intended for multiple occupants are usually at least eight feet. People over six feet tall are not going to be comfortable on the smallest size hammocks, but this should not normally be an issue in terms of comfort.
Overall length tends to have the most significant impact on comfort. The overall length can limit how tight or loose the hammock is when hung up. Tight hammocks can be too rigid for people to get into comfortably. Loose hammocks can cause too much of a curve for users to feel comfortable while in the hammock. The overall length only becomes an issue if you cannot vary the length of the trees or posts being used to hang it. Changing to a larger overall hammock length is better if your current hammock is too tight, while shorter hammocks are better if the hammock is too loose.
Spreader bars are the wood bars at the end of some hammocks. The presence or absence of these bars alters the ideal distance between which it should be hung. Switching between a hammock with spreader bars and without can allow the same sized hammock to be more comfortably in the same location. Hammocks with spreader bars should be hung between posts that are at least as far apart as the total length of the hammock, but ideally is about a foot longer than the total length. A hammock without spreader bars should be hung between a distance about 90 percent the total length of the hammock. A 15-foot hammock with spreader bars would be comfortable between two trees that are 16 feet apart, while a 15-foot hammock without spreader bars would be comfortable between two trees that are 13.5 feet apart.
The length of the hammock contributes a significant amount to how comfortable a hammock is, but it is not the only factor. Material has a subjective impact on the comfort of the hammock. A solid weave might be preferable for some people, while rope hammocks appeal to others. The width has an impact if several people use the hammock at the same time. You want to use a hammock at least five feet in width if you want several people to comfortably use it at once.