I was able to connect the single column and add enough extra constraints, such as Fixed Rotation, and Displacement of X and Z = 0 on a few nodes to limit the spring to motion along the Y axis without having to make more columns. To simplify as much as possible, I used a linear material, Stainless Steel, which is a lot stiffer than the TPU, but I put a lot more mass on the top to get the deformation to the flat part of the Force Deflection curve. It is not quite flat because there is a mistake I found later that I haven't fixed yet.
The good news is that when I turned on Gravity, the solver pulled the top down to the same deflection. I ran a Modal analysis, and found the first mode was at 12 Hz. I made a three step transient, step 1 gravity in 0.1 s, step 2, no change till 0.2 s, step 3 a 12 Hz 4 mm sinusoidal base motion will 1.2 s. I got a result similar to what the paper shows, excellent isolation. Because there were so few nodes, the Transient solution finished in 9 minutes! Before I was waiting hours.
I checked the Connection Elements created by the fixed joints and see I made one mistake and have one extra edge that I will remove and rerun the analysis to get final results.
I think you can get to this point (without the mistake) by Monday.