"only sufficient" is correct and usable in written English.
You can use it to emphasize that it is not more than sufficient, but just enough. For example: "We only had sufficient resources to complete the project."
-- the one and only, sufficient unto himself, outside the action, uniquely immobile!
An ingrained competitiveness was only sufficient to put United level for a while.
The road up the bank is narrow and only sufficient for one cart.
On the ground it is only sufficient to ensure the impermeability condition.
These latter ones give only sufficient conditions to ensure the quadratic stabilization.
However that inequality is only sufficient, which could potentially be conservative.
"To imprison someone for a long prison term, it is only sufficient to have his confession.
But what was fantastic for Mr. Armstrong and FM radio is only sufficient as a stopgap today.
The 27 member states need only "sufficient progress" to be made by the next European council summit.
Moreover, we showed the complex dependencies of cortico-striatal plasticity are not only sufficient but necessary for learning and extinction.
The transparent tile provides not only sufficient daylight for housing but also helps in increasing the ventilation rate.
