Aftermarket will be the easiest option. Get two doorlock actuators, momentary lock switches, and lots of wire. You can actually purchase a kit that come with everything needed from most car audio and alarm shops. Probably under $100 too.
the hardest part is just mounting the actuators and sometimes getting the wires through the boots in the door. First door takes a little while 2nd door is always easier. The factory switches can be used if you want because they do all the work in the system, there are no relays. Look for a 5-wire system and you can integrate them into it although it isn't necessarily for the beginner in wiring/electronics and you might want to find a local audio place to save you the trouble.
The wiring that we have in our cars for the factory door-locks is actually the hardest of the wiring systems to integrate into. You need to be able to first find the wires but then you will need to diagnose which is the master switch and which is the slave and then insert some relays correctly facing the right direction. IF you do not you will blow part of the factory system, its a pretty good pop and you will hear it if it happens.