In my imagination, Murderbot looked kinda like the player character from the game 'Citizen Sleeper', pictured below.
Which is to say, very androgynous and very obviously cybernetic.
There's quite a bit of character similarity between them too, because the titular Sleeper is a human consciousness in a cybernetic body that has a lot of biological parts, and they are kept loyal to the company who owns them by a drug that will cause their body to break down if they stop taking it. Same intent as the governor module, but a different approach.
I found Murderbot's physical appearance an important aspect of the books, not just for surface plot reasons (everyone knows they are a bot etc) but because it's a large part of what people need to overcome from the perspective of seeing past their prejudices.
