I
Think I would turn the basket upside down and make a pattern with seam allowance. Then, measure from the top to the bottom of the basket with seam allowance. Seam the inside fabric to make a tube. Then, pin the bottom to the to the side piece ( the tube). Stitch carefully until you have stitched all around. Try it all around for size and then resew again for strength. You may need to glue the top. It is a beautiful basket and would look great as a towel holder. Shoot us a picture when you have finished.