The largest (USM-VB) would be the most suitable solution for the M50:
Description: InVision USM-VB
Order Code: 044912
Web link: www.rycote.com/products/044912
As the microphone is 800g, you may find that using it in a horizontal position will cause it to sag. This won’t be a problem providing the inner support ring does not touch the outer support ring.