Yes—extension tubes/bellows can increase magnification, and under the right conditions all three methods you listed can be used to get more magnification.

Which works best depends on the specific lenses, focal lengths, and how much working distance you can tolerate. In general:

• extension tubes or bellows increase lens-to-sensor distance, which raises magnification
• coupling/stacking lenses can also raise magnification, but behavior depends strongly on the focal lengths involved
• adding another lens between camera and reversed lens may help, but the result is highly setup-dependent

The tradeoff is working distance: as magnification goes up, usable distance to the subject usually gets smaller. Physical size of the lenses/tubes can also become a limit.

So there isn’t one universally best method. If your goal is simply more magnification with a reversed lens, extension tubes or an auto bellows are a standard, practical starting point. Beyond that, compare setups based on the exact lenses you have and the working distance you need.