I'm sorry to welcome you to the club, but as Dx's go, yours ain't too bad. I'd recommend that your first order of business be to get a second reading on your biopsy. Gleason grading is almost an art and there are a few labs that specialize in it, like Bostwick or Epstein. You don't wan't to overreact to something that isn't really there or vice versa.
The last thing you want to do is jump into a hasty decision now while you are in "cancer panic" mode. Know that you have plenty of time to make a decision, and it will be up to you to learn about the alternatives, their curative power and their side effects. Doctors will almost always recommend whatever they specialize in -- surgeons recommend surgery, brachytherapists recommend brachy, etc.
Assuming it's confirmed, and that you have an insignificant amount of low grade cancer that may never become a problem, Active Surveillance is certainly a great choice. You have many years to live, so why not live them symptom-free for as long as you can, perhaps for your entire life? You can always treat later if it progresses, and by surveying it actively, you'll know when that is.
Because you have so little involvement, focal therapy is also a possibility for you. That means they image and treat just the cancer and leave the rest of the gland intact. Because PC is usually multifocal, it may not cure you, but may buy you more time on AS. Imaging techniques are improving and there are a few experts at certain kinds.
If you eventually decide to pursue radical (whole gland) therapy, all of the following have 95+% cure rates in the hands of the best practitioners for low risk disease like yours:
- Surgery (robotic, lap or open)
- SBRT (CyberKnife)
- HDR brachytherapy (temporary implants)
- LDR brachytherapy (permanent seeds)
With cure rates that high, you can be reasonably assured that the problem will be fixed once and for all. While their cure rates are equivalent, their typical side effect profiles are different, especially surgery. I won't overload you with details about them now, and some may not be available to you where you live. Just know that there are many more alternatives than your urologist seems to be familiar with, and you have time to investigate and interview several doctors. I talked to 5 specialists over 6 months before I made up my mind.
Please feel free to ask questions whenever you are ready.