Here's my tale in bullet points:
- Bought a chair to support up to 400lbs.
- I weight 320.
- Hydraulics lasted 3.5 years, died a month or two back.
- Bought replacement. Lasted a month and change.
- Can't get replacement off.
- Printed this set of interlocking vertebrae and cushions.
They work pretty well for my chair so far. You may want to scale up or down depending on your chair, these print as-is with a diameter of 38.5mm.
The A and B pieces interlock, and have tolerance at about 0.3mm. This can be printed in PLA, but I recommend ABS or PETG above all else. About 15% infill should be fine, if you can do the tetra-infill from Cura, I'd go with that maybe.
The Cushion piece I printed in Ninjaflex, and I'd recommend that or another very flexible (not semi) material. That may be printed at about 15-30% infill. I went with 20.
Holds up well so far :)
Monoprice MP Select Mini V1
The Cushion piece I printed in Ninjaflex, and should be a flex material.
The A and B pieces interlock, and I recommend ABS or PETG above all else.