I chose this Fanatec Club Sport Shifter 1.5 because, from my knowledge, it's the only shifter that can convert from H-gate to sequential mode in a few seconds, without having to use any tool.
I mounted the shifter on the tube of the seat with 2 bicycle camera mount modified to use the T-nut provided with the shifter that goes into the shifter's grooves.
The shifter is well fixed. It's moving a little bit when shifting but you don't feel it when driving.
I improved the fixing with using the whole bicycle mount. Before I have to remove a part because my bolts where too short. I ordered M5x35mm hex head screw, and now I can use the whole part so the shifter will be less closer to the seat, and better tighten to the seat.
I update the fixation to the chassis with professional clamp and aluminium profile to get a perfect rigidity.