On this topic, I have a lesson learned. I bought this one:
However, it is not what I would consider “low” profile. I remove my supplementary waste board to use it, and it gives me a small amount of clearance between its top and the bottom of the X-rail. I haven’t measured but I can get maybe 1" or a little more. In order to use it with my current setup, I have to raise my router very high in the mount to give me enough room for Z travel and retract height. I eventually plan on moving to a ball screw Z-axis anyway, so that won’t be a problem forever.
It is however very stout, and heavy duty in terms of hobby use. It should provide me easily a decade or more of use, and is applicable for other things outside of use for the SO3. But “low” it is not. Buyer beware.