The problem with tongue extensions is you can't extend a trailer tongue with off the shelf, bolt on parts. To do it "right" you need to have the extension properly designed for the trailer and properly installed by someone skilled in the art and science of welding. It's not something you can just do in your garage with a $90 Harbor Freight flux core welder.
On the other hand, receiver extensions are somewhat widely available, and are a simple bolt-on solution.
If you have a 2-1/2" square receiver, I would get a Curt weldable receiver tube of the appropriate length, drill a 5/8" cross hole to secure it in the receiver at the proper length, and install your 2" shank in that.
That's what I did. It's very strong, secure, and slop free. I've towed as much as 800lbs of tongue weight, and easily 6000lbs of trailer, with it at 12" with no noticeable deflection.