I'm confused as to what you mean here. You can take the dash action at any point during your turn as long as you haven't already used your action. You can move, then take the dash action, and continue moving with the extra movement given by the dash action.
Hello,
If you are correct : that is, if in the current version of BG3, you can do the Dash Action anytime (before, during or after a Move), then my suggestion is needless and all is good. From the gameplay video, I had the distinct impression that you could not choose to Dash after starting your Move, but I could be wrong.
About "double Dash" : a Rogue or Monk can both use the Dash Action and their special extra Dash Bonus Action.
