I designed this because the existing models on the internet were either paid or not well made.

It fits snugly and does not slide off. The current version turned out to be slightly smaller than expected, but it still fits my (average size) hands quite well. You can easily edit the model's parameters with a personal OnShape account to better fit your needs (see link below). I might integrate a stand in the future.

Recommended settings:

• Nozzle: 0.6 mm
• Material: PETG
• Layer height: 0.3 - 0.4 mm
• Supports: organic
• Infill: 10% - 15%
• Top fill pattern: concentric
• Perimiters: 2 - 3
• Seam position: rear (or drawn manually)
• Orientation: feet on built plate (other way around might work too), if the built plate is moving like on the Prusa Mini, orient it such that it can't get knocked over (see screenshot above). 

Prints in under 3 hours on my Prusa Mini.

Model on OnShape: https://cad.onshape.com/documents/53f096ad806e96813a732722/v/fd2524880804ba6935ea9840/e/e4425ab148cb26