No! What you say is "not true at all".
The only "just right" supply of money is that which the free market determines is "just right". The government cannot determine it for us.
If you believe it can, then you must examine your premises. They seem to land heavily on the planned-economy side.
If the free market supplies the "just right" amount now and in the future supplies less, deflation can result.
Why does that make deflation a good thing?