You do not necessarily need a transformer. There are also head amps, or pre-preamps, that will provide the necessary gain to allow an MM phono stage to work with a low output MC cart. Many hear will tell you that there are inherent issues iwth a step-up transformer that would point you to an active gain stage (aka head amp, aka pre-preamp). whatever you get should have provisions for optimizing the loading to get the most of your new cart. And if your physical space requires long cabling for the xformer, that is also a factor, as the multiplication factor also "applies" to the cables.
Phono Preamp Vs. Transformer for Moving Coil
I have a Koetsu Black and am currently using a Creek OBH9. Loaded at 1000 ohms. The Creek is not adjustable and I believe that optimal loading is 100 ohms for the koetsu. I am getting good sound but in discussions with other members in the forum believe I am losing out on some quality. I have a Conrad Johnson PV11 that has a great phono stage. Is it better to go for an external phono preamp or Transformer and plug into my phono stage? I hear differing opinions.