How much surgery do you not want?
You can definitely get away without holes being cut in the sides of the guitar. In most cases you will need to fit an end pin with a jack plug to get a neat installation, but you can do without in the case of sound hole pickups - route the cable out of the hole and over the top.
The most common solution is the under saddle transducer (UST). That will require a slot and a hole in the bridge.
Microphones... these are sometimes mounted on goose necks (which require securing to the body) but not always. I have the Baggs Dual Source in both my flat tops, and that has the microphone in a little cube of foam that's fixed inside the back of the guitar with double-sided tape. The Baggs Anthem has the microphone inside a capsule that is fixed on the inside of the guitar under the saddle.
All the different types of pickups have pros and cons. The most commonly used are the USTs which have a lot of definition and good bottom end, but also can sound a little mechanical (though they are getting a lot better). They also are fairly feedback resistant. This is a very common sound that you hear a lot on records and especially live recordings.
The sound hole pickups are getting quite sophisticated. The Baggs M1 has two coils, but they are stacked, and the bottom coil has some movement and picks up vibrations from the top and adds these into the mix. This type of pick up is fairly feedback resistant, good for high volume applications.
My opinion is that if you want fidelity of sound then you start getting that when you combine two different types. I have UST and internal mic fitted to my flat tops - the Baggs Dual Source system. Baggs also offer the i-Mix which combines a UST with their i-Beam bridge plate transducer.
Most systems will require a battery, and mixing (dual pickup) systems will usually require some sort of pre-amp module. These can be fitted non-destructively, as can the controls. Here's a picture of my Larrivee with the controls and module visible.
The controls (in this case mix and volume) are on a little plate that is fitted inside the sound hole.
Baggs is easily available in SA. Fishman is another option with a good reputation, though I don't have personal experience. A VERY good sound hole pickup is the Sunrise, though they're not easy to come by and probably not cheap.
Expense is always a factor as well. The mixing systems will set you back a bit. The out of box Baggs Dual Source you get here is UST and mic, but Baggs can provide the components separately so you can combine sound hole pickup (not necessarily theirs) with the mic.
There are very good systems available these days - especially if you want to spend some money ? Add in a good out board pre-amp/DI (D-tar, Baggs Para-DI) and you can get a very good, convincing sound. Or there's a Fishman box that uses modelling to reproduce "classic" acoustic guitar sounds.
The last few years I've heard some guys in concert with superb acoustic guitar sounds.
No need to be a purist! In my book using FX with an amplified acoustic is quite acceptable.
