You would need to purchase a base such as Augeo - the ratio is usually 25% oil to 75% base.
Example - For a 100ml bottle, you would add 75ml base and 25ml oil. These require testing to see if 25% oil is right or too much. You can use from 15-25% oil and just adjust your base accordingly.
You can find our available diffuser bases here - https://craftovator.co.uk/collections/diffuser-bases