I'm writing a gamebook using the textadventure mode because it has more options.

I want the player to write down a number. for this case, the character's preferred height. since listing out the the selectable heights would look a mess on the screen, I was thinking of getting them to write it down, like 6'2" or 4'10"
(I'm not sure if that is a good or bad idea)

the command bar seems to either stay permanently or not at all. is there a way to hide it for all rooms except this one?

Now that I am looking, you say you are working on the gamebook, which is something I don't know anything about. I was using the other part of the system. What can the gamebook do?

I'm writing a gamebook, which is a non-linear story with choices and text adventure's ability to track achievements and keep score. a mess of player stats (health, magic etc) and visible object inventory to keep track of what the player has on their person, and if scripts and conditions with which the player discovers specific story paths.

Also I did more digging in the forums and found the way to make the command bar temporarily visible!
https://textadventures.co.uk/forum/quest/topic/4853/showing-hiding-the-command-bar

I decided to just add specific height options to click on, but the command bar option is useful in getting players to choose their own names.

That's actually, if from a different page, the answer I had posted earlier, before I realized you had specified for "gamebook" which I had never used because of what seemed like fewer options, although you said there were more, so maybe there are more instead. It seems the two systems use the exact same script.