In TF2 you can bind a single key to crouch jump.
The console command for jump is +jump & the command for crouch is +duck
A + in front of any command means that it will execute for as long as the button is being pressed if at all possible..
You can combine jump & duck to be used with a single key super easily. To do so simple launch TF2, open the console & then type the following three lines in one by one, pressing enter after each one.
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alias +cjump "+jump;+duck"
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alias -cjump "-jump;-duck"
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bind space +cjump
If you've entered everything correctly you should now be able to crouch jump with a single key press..