Remember the Mini came in 12° 14° and 16° models and had a 43.5″ shaft. If you want something like that a custom-fitted M4 fairway might be about right except it will probably offer even more ballspeed and forgiveness.
This extra degree of strength allows for a thinner more flexible clubface and enhanced ball speed at impact. The thinner clubface along with a new hidden micro-slot in the sole not only increases COR but also expands the effective hitting area across a larger area. The micro-slot also allows for more weight to be redistributed for a lower and deeper CG location yielding improved launch on mid and long iron shots.
Start at address so you can ensure that you have a flatstick that fits your body and posture. Unlike full-swing clubs that droop and bend significantly in a dynamic motion putters stay about the same during the stroke so getting a length and loft that complement your setup is an important first step.