of all the line on the boat, this line means the least. use the cheapest (although light would be good) line you can find. 1/8 if your hands can tolerate it. no bigger than 5/32. go with a few feet over twice the length of the mast. I guess it would be good to have a line that doesn't absorb water too.
something like this would work...
https://store.catsailor.com/pc/viewPrd.asp?idcategory=550&idproduct=30426

or

https://store.catsailor.com/pc/viewPrd.asp?idcategory=562&idproduct=8245