Do I need to buy a 135mm F/2L!

135mm on a full frame camera is a good portrait length, although 85mm is also good. In the case of this focal length you only have the choice of the 135mm f/2L for about $1000 or the new Carl Zeiss 135mm f/2.0 APO which is not out yet and is over $2000. I expect the Zeiss might be a bit sharper but it is manual focus and twice as much money.

So if you want the 135mm focal length, the Canon L seems like a good choice.

The cheap option is to get a Zeiss M42 mount lens, the old Zeiss Jena 135mm f/3.5 MC is a very good lens, but is also manual focus and would require an adaptor.