When needed a cotton for a wool top just brough it and found the matching orange colour which I thought won't be easy. Sometimes they have good prices so worth having a look. The store is big so if you don't know what you need then you will have to have some spare time to look inside.
Generally the service in the dress fabric department isn't great and occasionally it's appalling. I've found the furnishing fabric staff much more helpful but unfortunately I sew clothes so I'm mostly wanting to shop for dress fabrics. I'm not sure if the staff actually have any sewing knowledge or experience. A young staff member one day didn't know what fabric grain is! I have given up buying fabric from Spotlight because they're so stingy they can't even give you an extra centimetre and sometimes one edge of the fabric is shorter than what you've paid for and often it's been cut off grain which makes cutting your garment challenging. I've even had a staff member cut off 10 or 20cm of fabric with a flaw in it before cutting the piece I want rather than just giving me that piece at no charge, like they do at every other fabric shop! I prefer to go next door to The Fabric Warehouse where the staff are better and they're generous cutters.