I had two pfizer vaccine doses but then got break through covid in august. should i now get the booster also? or does breakthroughs infection act as booster?

Get the booster as there are no guarantees that your antibodies produced by the breakthrough infection were robust or still effective.

A booster is the best way to build up more antibodies .Even with a booster you can still get a breakthrough, you had the vaccine twice and still got a breakthrough. The more antibodies you have the chances if reinfected, the less the symptoms you will suffer .Always take precautions, wear a mask and stay away from those you don't know.