Try well aged hard cheese, most of the lactose is processed by the microbes. Naturally fermented yogurt is also low in lactose, but it needs to be thick and only 2 ingredients (milk and culture), if it is runny or has thickeners, avoid.

Good quality butter also has minimal lactose. It should basically be 100% fat.

Be careful though, it may be a dairy protein intolerance rather than lactose, usually this is more severe.