I have lined baskets before and what I do is trace the bottom of the basket but make it a bit bigger for seam allowance. Start with that, then wrap your fabric around the outside of the basket and make it about that size or a tad larger, as you can always take in the side seam. Make it taller than the basket also, so you have room to turn it under and make an elastic pocket and have enough at the bottom to stitch it to your base circle. So better to be a little taller than you need than too short. Good luck and show us pictures.