This article explains how to make your own avocado mayo. You can use avocado oil, canola oil or olive oil. You can also use avocado Mayonnaise or avocado sleuth to make your own.
Avocados are available in a variety of FODMAP-friendly serving sizes. Therefore, there is no harm in limiting yourself to one avocado serving a day.
Avocado oil may be a healthier alternative to regular mayonnaise. However, the evidence for this is mixed. There is a multitude of evidence to support the nutritional value of avocado oil.