Here are pics of what real sailors (aka privateers) wore during the Elizabethan time period, from period sources. The men for the most part are wearing Venetians.
www.kimiko1.com/research-1...riners.html

What you are looking for in its simplest form are called "slops". Women might have worn Italian "drawers" that are shaped similarly, sorta. The simplest pattern is to take pajama pants pattern from one of the Big3 pattern company at 99 cents, and cut off the bottoms below the knee. It will not be perfect or period, but it's doable. The upper part would be a bit bigger, so you could slash and spread the top before making up the slops or drawers.

you can make the ungathered bloomers by using the same pattern and just not gathering them.