I think you will find that regenerative braking is not simply shorting the motor with a FET. Maybe a small toy motor, but a motor of any size is going to detonate your FETs. It can only end in tears.
You need a fairly decent sized resistor to dissipate the heat. It will all depend on the time required to stop the motor, the rate at which it is going to be stopped, etc.
Perfect example, many subway systems use series/parallel configured DC motors, series to get moving, parallel for speed. The braking is handled in a similar way, progressive increase in the resistive load. Braking is regenerative, with many banks of spiral wound metal resistors the size of your forearm. They look like heating coils, and essentially become that. The heat generated is used for heating the train cabin in winter. Even in industrial settings where motors use regenerative breaking, the resistors are big.