I find following a pattern difficult and, to be honest, sort of boring so I make things up as I go. Don’t be too impressed though, the dividers are dang easy. There are a lot of online calculators that automatically figure out diameter of a circle based on the circumference measurement if you want absolute precision but I just use a tape measure and eyeball it.
Cut 2 pieces of very heavy non-woven inferfacing the exact diameter length of the bottom of the basket and as tall as you want the dividers to be. Cut 2 pieces of fabric twice as wide and added a seam allowance of about 5/8" all the way around. Fuse the interfacing right at the fold line.
Fold the fabric wrong sides together and sew down both sides half way between the edge of the fabric and the edge of the interfacing. This little bit of extra fabric leaves something to stitch to the basket lining, you’ll see more about this is a sec.
also sew about an inch or so along the bottom beside the corners right along the edge of the interfacing. You are stitching the corners here and leaving a small opening at the very bottom to turn the rectangles right side out.
Once turned right side out, taking care to poke out the corners, press and stitch along the bottom of the rectangles to close the opening. Now stack both pieces and stitch exactly down the middle from top to bottom.
Press to get a crisp cross shape. Now the edges are not full of stiff interfacing, they are quite pliable and easy to sew to the basket lining. Mark the lining in quarters taking into consideration the seam allowance. You are going to catch the last side of this cross shape in the seam allowance of the lining.