I needed some simple pots that could fit into nice ceramic pots I had where no store bought inner pots would ever fit. I found the following nice model: https://www.printables.com/model/65317-parametric-inner-flower-pot-with-stand, but the parameters were tweaked in Fusion 360, a piece of software I don't have. I figured the model was very simple, so I recreated something very similar in FreeCAD.
The intention is that you download the FreeCAD file and tweak the parameters in the Parameters
spreadsheet in the file in order to fit your particular pot.
The intention is that you glue the legs to the pot. Had to be two separate parts just to print as cleanly as possible.
I also uploaded some example STLs, so the model becomes viewable here on printables. I doubt that particular pot size will fit your needs, unless we happen to own the very same strangely sized ceramic pots ;)
The pot in the image is printed using Mystical Green PLA Prusament with a 0.6mm nozzle and a large layer height. I don't think the material used here matters a whole lot, but I do recommend a large nozzle and large layer height for faster printing and higher likelihood of being waterproof.
The author hasn't provided the model origin yet.