You would expect a floatation suit (overall) to be warmer than a two piece, and (in the case of you falling in) to protect you better from hypothermia and to provide good support.
There arent a great number of these suits being marketed for sailors, but there are some, . . . . heres two examples . .
Definitely being targeted at sailors, . . . . but according to this report (its a pdf file)
These suits are counterproductive, they have dangerous design flaws, and the concept of a floatation suit itself would even appear to be inherently dangerous. . . . . the two previous examples advertised are mentioned by name in the report, and are poorly recieved.
Perhaps more up to date designs are better . . . . . but the report makes worrying reading.