Do you mean just for conditioning to wash off after?
You could try Hairdressers Invisible Oil Pre-Shampoo Hair Mask - . - Bumble and Bumble which is a brand highly recommended.
If you want something simpler/cheaper I'd recommend trying either castor oil or coconut oil . I use SheaMoisture as a brand myself, you can browse their products and see if something takes your fancy. Just mind you that some people's hair doesn't like coconut oil and your hair may go a bit straw like.