I wanted to place an order for some new jerseys for the Holidays, and I just noticed that Umbro uses chest sizing numerals, as opposed to the traditional S-M-L-etc. I wear a medium in Adidas and Nike, and a random blog online said this is a 38 or 40 in Umbro. Mediums are comfortably loose on me. Anybody have any advice in choosing the correct size between the two? Or any advice on Umbro shirt sizing in general? Much appreciated!