Digital temp control is part of the air-con system. Yes you can retro fit the air con with climate, but it is a very large job. You need to fit the compressor with brackets to the engine, condensing rad with pipes, acumulator and pipes, electronic interior air direction flaps and motors, relays, wiring, cabin temp sensors and probably a bunch of other stuff.
This is one of those conversions where it is easier sell your current car and buy one with air con, or buy a complete smashed donor car and swap the whole kit over.