I hear you - I always aim to use a white batting when there is a lot of white in the quilt. Have you checked this site? They purchased most of the boundless fabric and sell it at $5 a yard. I have purchased multiple items from them and have been very pleased - my only thought is boundless fabric is a bit on the thicker side
https://www.quiltingcat.com/collecti...y=best-selling
Another option might be a 108 from Marshal Dry Goods ..... and it is at a great price point
https://marshalldrygoods.com/product...-cotton-solid/