A third rail or geared focusing stage can definitely help. Move the entire rig closer to or further from your subject to focus. But, geared focusing stages are pricey and add a lot of bulk and weight.
A "poor man's" focusing stage is simply an extra long Arca Swiss type lens plate on a compatible quick release platform. Loosen the release enough to allow you to slide the rig forward and backward to focus.
Or just put everything on a monopod and lean forward or backward to focus. It helps to have a ballhead on the monopod to allow you to tilt, too.
A bellows is nothing more than an extra long, variable extension tube. It allows for more extension than is possible with most fixed extension tubes, so allows for higher magnification.
A 135mm lens is a fairly long focal length to use for macro shooting, especially on a crop sensor camera. It's harder to hold steady and you need to stop down a lot to get any depth of field. You might find yourself using f22 or smaller, if the lens allows it. Plus you have to factor in for light fall off behind the lens. The longer the lens focal length, the more extension you need to get to 1:1 magnification (in general... not all lenses are created equal... this is effected by the lens' minimum focusing distance).
You might try the bellows with a 50mm lens. It will be a lot easier to handle and won't need as much extension, unless you are looking to do really high magnification shots.