Yes, you should be able to use a commercially available USB to RS-232 serial converter/adapter.I mean simple USB to serial converter which is just locally available one
Breakout board, Is this special kind of board
Currently I am using PuTTy for PC interface. If I used USB to serial converter then, can I use PuTTy ?
And Yes, you shouldn't have any problems using the converter/adapter with Putty.
I regularly use such a configuration with Putty when developing embedded applications.
The only issues with some USB to RS-232 serial converter/adapter is many of the less expensive units do not offer all the lines required for full hardware handshaking.
As it appears you are not using hardware handshaking, it should be an issue even with the less expensive models.