LMR62421 Inductor selection for boost application
Or are there any downsides of using bigger inductors then you need in boost applications (other then the cost of components)?


Certainly (aside from size and weight), an inductor with higher inductance will typically have more turns – and thus, more ohmic resistance, and thus, more loss (unless you also make the wire diameter larger, which makes the inductor even bigger and so on).

TI has an excellent design calculator on its homepage. Use it. The "Mobile/iPad version" works without adobe flash. I don't know why someone would use adobe flash for this, but TI does. When you use it, it will give you the component values as well as component recommendations.