There are a few silent systems available. They install optical/mechanical sensors under the keys to register your playing, and these report to a small control box with headphone, volume control, MIDI out, etc.
In order to mute the sound of the acoustic, the hammers are stopped before the strings either with a felt strip or a bar that stops the hammer shank. Most of these systems modify the action of the acoustic so it plays (a little) worse even in acoustic mode in order to make room for the hammer stopping.
If properly installed and calibrated they can be pretty good, but none of them will out-of-the-box work as good as a proper digital piano purely from a MIDI controlling point of view. Expect a few days of painstaking calibration until you're satisfied.
The cheapest quote I got here in Germany was around €1500 including installation in an upright.
If you want unmodified touch on a grand piano, along with continuous pedalling (not just pedal down/up but half-pedalling as well), USB and MIDI Out, the quote I got was 3500€ (around $4800), which is more than some new acoustic pianos sell for and certainly more than most digitals... And I am still considering it