You will lose information if you convert 0-255 to 16-235, no way around that. 
You could use:
a. Color->Basic->Levels and map the 0-255 input to 16-235 output.
b. Color->Basic->Limiter 16-235 to simply cut off the values.
c. Color->SmoothLevels to do something like Levels does, but with more control over the mapping.
Important: if you use a format that support VUI tagging, make sure that it is configured correctly.
https://en.wikipedia.org/wiki/Colour_banding
Dithering = adding grain, can be archived by a. directly adding grain or use a debanding filter to add the grain mainly in uniform color sections.
Cu Selur
You could use:
a. Color->Basic->Levels and map the 0-255 input to 16-235 output.
b. Color->Basic->Limiter 16-235 to simply cut off the values.
c. Color->SmoothLevels to do something like Levels does, but with more control over the mapping.
Important: if you use a format that support VUI tagging, make sure that it is configured correctly.
Quote:I got very bad looking color banding on uniform surfacesThat sounds more like an issue since you used 8bit encoding without dithering, HEVC unlike H.264 supports 10bit in its main profile, so basically any decoder supports 10bit for HEVC.
https://en.wikipedia.org/wiki/Colour_banding
Dithering = adding grain, can be archived by a. directly adding grain or use a debanding filter to add the grain mainly in uniform color sections.
Cu Selur