Which end mill to level my acrylic bed?

[HankMcSpank]

My CNC has an aluminium bed, but it's not completel;y flat...don';t fancy levelling that, so intend bolting some 5mm acrylic sheet onto it.

The largest internal diameter collet my spindle accepts is 6mm....there's a bewildering array of endmill, materials, flutes etc.....could someone recommend one that would be a good candidate to level acrylic?

Thanks.