The 120 Makro Planar is an excellent choice. It will focus down to 0.8m (1:4.5 magnification) on its own. With the 32mm extension tube it goes down to 1:2.
Don't use shorter extension tubes, they buy you very little. It's designed for the 32mm.
Avoid the 135mm lens. It has no focusing helicoid. It's designed to be used with a bellows, and won't work without one ($$$). Excellent lens however.
I have both the 120mm and the 150mm, and use the 120mm for close subjects almost exclusively.
BTW, a comment on lens "optimization".
Many lenses, particularly those for close work, are said to be optimized for a particular range of magnifications, like "2:1 to 1:10" or some such.
This does NOT imply that the lens will fail to perform satisfactory when used at other distances.
Most Makro lenses, and particularly the Hasselblad 120mm Makro, are stellar with all subjects.
- Leigh